Leave stuff like ratios of reproductive sex alone; I don't think this is a direct obstacle to something people'd recognize as a utopia.
Divide the Earth up by ecoregions. Extensive surveys of natural resources, landforms, biomes, economically-significant species, ecosystem-provided services, existing human use and infrastructure, so on. "Urban" counts as a biome here.
Priority technologies to research, develop and deploy as universally-accessible things:
-Passive or solar-charged night-vision glasses. This is to reduce the need for artificial electric lighting at night; its creation was a real game-changer, but the energy consumption is extreme.
-A reversible, safe, efficient oral contraceptive for folks with danglybits. This is to be paired with widespread distribution of existing birth-control methods.
-Dump tons of money into research for efficient hydrogen-fuelled and electric transport; also kick off a nuclear renaissance with an emphasis on modern design and organizing/management principles without the neglect incentives currently possessed by private industrial NPOs. Expand supplemental renewables production. Every continent gets an elevated high-speed rail network.
Relocalize culture. Start with food. Create new or revived forms of cuisine and food culture that are specific to an area; identify candidate wild foods and likely yields, promote them vigorously, and incorporate them into the diet; initially as supplemental or occasional foods, but with an eye towards transition to primarily-local resources. This model is not even vaguely allergic to agriculture, but it is focused on providing food for local people in a sustainable manner rather than engaging in high-volume agricultural trade. Over-bred domestic animal stocks designed for factory-farming will be phased out. More robust, mixed-trait varietals will be emphasized, as will best practices for handling (some of Temple Grandin's work is useful to this idea). Wild stock in general will be promoted, though the development of sustainable populations and management programs for harvesting may take a bit. One sort of long-distance agribusiness trade that may be a good idea is crops and livestock from similar biomes, in an effort to maximize productivity. Focus on more microlivestock as well, up to and including bugs. Then take all of it and that have each bioregion figure out a pretty good diet that balances nutrient needs and caloric abundance during the critical phases of childhood, design a local cuisine, and go.
Some areas simply won't be compatible with settled habitation, even after all that. So create some technologies to facilitate a sort of moden nomadism -- the modern Inuit would probably be a lot better off if, like their ancestors, they were legally allowed to do mobile living with the kids and, as a consequence, get a diet rich in organ meats from local wildlife. Portable, clean electric generators, high-end durable vehicles of appropriate sorts, long-range communication technologies for areas off the beaten path, ubiquitous first-aid kits and training -- emphasis of state services in such areas should be on medical and emergency fast-response. Other important stuff: Rural communications and education.
Economics: Automate the hell out of whatever is amenable to having the hell automated out of it and still capable of producing a decent product. We don't get nanotech, but 3D printing is fair game -- subsidize it for startups.
I'm still chewing on to what degree the actual ownership vs management structures look like here, and have been writing this since I woke up. Will come back and poke it more in a bit...
EDIT: S'more thoughts on economics:
I'm envisioning a lot of production being done in a massively-automated fashion enabled by dedicated, highly-trained staff, who work for...well, call them concerns. They're kinda hard for me to pin down as purely state or private. It seems like a lot of frameworks could fit in here -- Jamais Cascio's "Robonomics" scenario, in which private companies who pay a flat income tax and obey regulatory restrictions but no payroll taxes could probably be slotted in as readily as an idealized "the state owns the means, cooperatives license them" sorta Marxist-like scenario. However you want to construct it, the goal is "productive economy to enable a measure of global trade and undergird a social support system" -- basically, I want to see free medical care (in terms of the end-user's experience of it), a basic income guaruntee, and support for other things that may not be immediately profitable in and of themselves but produce significant social value.
I've thought in a lot of situations about a two-tiered currency system: essentially, basic income guarantee, necessities, most manufactured goods and social services are payed for with one kind of currency; bespoke items, luxury goods, non-necessities and so on are payed for with another. Basically representing automated versus direct human labor.
Law enforcement: I don't see it disappearing given the constraints here, alas. Some remedies off the top of my head include an emphasis on beat cops who patrol their own living areas, and neighborhood police booths like in Japan (remove the social distance); backup in the form of general support for an area, but ultimately answerable to the local side of things. This is coupled with eliminating victimless crimes (drugs and sex work are immediate examples), and a prison system that looks a lot more like Norway's rehabilitation approach to things.
Ecology: no single unifying strategy here, but I don't think we have to consume everything; moreover, it's ecologically and economically beneficial not to. Rewilding is good for some areas and ecosystems, but sometimes we improve on them.
The net picture looks sorta like this, at least in my head:
-People are born into relatively healthy, prosperous communities that have no explicit need to travel, but travel is easy and affordable. Work is not the same thing as employment; the choice between starvation and an exploitative economic arrangement is absent. Basic needs are meet. Personal and cultural autonomy are both significant. Most people have enjoyable lives; people who don't fit where they are have some ability to get out of there and find a niche that suits them better. The economy chugs along pretty steadily most of the time, with few fantastic booms but few real crises. But it's not stagnant either -- this is a terrific climate for science and intellectual inquiry, as free time abounds for many and there is not so much pressure to choose between that and starving to death. People who like it competitive are free to try and get into a concern, but work and employment are not synonyms -- lots of people do socially-useful work without being employed. People who just don't like other people and want to bog off into the wilderness or something and rough it can do that -- and if they decide to come back later society is still there for them. There's still incentive to find something socially-, commercially- or academically-relevant to people because human labor is incentivized seperately from the production that drives the core economy; even if you just write poetry, someone might conceivably pay you a few human-dollars now and again for it -- human labor currency can sometimes behave like a reputation economy.
Less harm, less disutiility, higher average wellbeing, a rich and stimulating life for most people, good health, less basis for direct conflict...
(Oh, I can see issues. What about climate change? Reorganizing ecoregions is bound to upset more than a few applecarts -- it's very well and good to talk about a Northern Forager-styled society in the Great Lakes area, but what happens when winters become warm enough that maple syrup can't be produced? What kind of economic and social shakedowns result? This definitely needs to be explored in more depth than I can managed right now...)
This model is not even vaguely allergic to agriculture, but it is focused on providing food for local people in a sustainable manner rather than engaging in high-volume agricultural trade.
Localizing agriculture would be quite expensive in terms of resources, as would phasing out existing engineered varieties. I'd focus on removing current farm subsidies, which tend to overly promote factory-style agribusiness, and plow more resources into preserving existing varieties of crops and livestock. Other than that, though, I don't think changes are warranted.
Assume for the time being that it will forever remain beyond the scope of science to change Human Nature. AGI is also impossible, as is Nanotech, BioImmortality, and those things.
Douglas Adams mice finished their human experiment, giving to you, personally, the job of redesigning earth, and specially human society, according to your wildest utopian dreams, but you can't change the unchangeables above.
You can play with architecture, engineering, gender ratio, clothing, money, science grants, governments, feeding rituals, family constitution, the constitution itself, education, etc... Just don't forget if you slide something too far away from what our evolved brains were designed to accept, things may slide back, or instability and catastrophe may ensue.
Finally, if you are not the kind of utilitarian that assigns exactly the same amount of importance to your desires, and to that of others, I want you to create this Utopia for yourself, and your values, not everyone.
The point of this exercise is: The vast majority of folk not related to this community that I know, when asked about an ideal world, will not change human nature, or animal suffering, or things like that, they'll think about changing whatever the newspaper editors have been writing about last few weeks. I am wondering if there is symmetry here, and folks from this community here do not spend that much time thinking about those kinds of change which don't rely on transformative technologies. It is just an intuition pump, a gedankenexperiment if you will. Force your brain to face this counterfactual reality, and make the best world you can given those constraints. Maybe, if sufficiently many post here, the results might clarify something about CEV, or the sociology of LessWrongers...