Losing weight and becoming more fit will make you healthier and more attractive. You can't effectively gain muscle and lose weight at the same time. In your case losing weight should be the priority. To do this, start tracking absolutely everything you eat using one of the many free trackers available out there, and eat below your TDEE. Invest $10 in a digital scale so you can track more accurately. If you don't know what you should eat, read this. Exercise is helpful to your general health, but losing weight is almost entirely about diet. Practically all specialized diets are scams, so beware.
To improve your strength and fitness (and attractiveness), barbell training is one of the most effective and safest forms of exercise you can pursue. You should read Rippetoe's books, his programs are quite likely the best option for beginners. You can pursue weight training even while you lose weight, but you won't make as much progress.
For fashion, reddit is probably your best bet. Spending money on expensive brands won't help.
If you want to target success with women in particular, PUA is a better option than the alternatives. Many people dislike it, but it is currently the closest thing to a science there is in the field. The basic idea is to simply make you try more often. That alone will tend to improve your social skills, and success.
Don't use success with women as a measure for your success. Attraction is based on irrational, primal emotions, and neither women or men, nor rationalists, care to even try and change this. The fact that women are not attracted to you conveys very little useful information. It is better to pursue your goals in order to improve your life in general. Losing weight and becoming fit will improve your quality of life far beyond attractiveness.
I have intentionally kept this short and skipped many details and arguments. Hopefully you can benefit from these as guidelines while improving your life.
You can't effectively gain muscle and lose weight at the same time.
This is commonly repeated, but not actually true for people who're just starting out on exercise. It's only when you've already reached a substantial level of fitness that it becomes an either/or proposition.
If you're already heavily overweight though, you're probably better off focusing on losing fat faster rather than worrying about building up muscle at the same time. You may already have a fair amount of muscle under there just from moving around your own body weight.
I want to spend a substantial fraction of my time optimizing myself in the direction of being more attractive to females, and I'd really appreciate your suggestions on how to do so.
Why
It should be pretty self-explanatory, but in case you're wondering: relationships are a big part of personal happiness, and where I am now, I feel more inclined toward increasing the number and variability of short- or middle-term sexual relationships rather than just picking a girl who wants to be my wife and run with it. But at the moment women aren't exactly chasing me down the streets, so I want to offer them a more pleasant experience of my company than what it already is.
Mind-killing
I sincerely think this post should provoke none of the above. I'm not asking for ways to trick women into liking me, nor about gender differences about what males prefer over females, etc. Please try really hard to avoid mind-killing subjects into your comments. I'm 'just' asking for ways to change myself into being a more sexually attractive human being.
Caveat(s)
I'm aware of the dichotomy lying around: attraction can be created vs attraction can only be amplified. In both cases there should be at least something that can be done.
I'm also aware that some people strongly dislike posts full of personal details, so I will try to keep them at minimum, while at the same time trying to provide the necessary description of my situation.
I would like
Try to aim for advice on stable improvements, about aspects that are proven to be sexually attractive to straight females, in the age range of 20 to 40.
For example, I know that height or facial symmetry are proven to result universally attractive, but I cannot really change that, and sole-lifts or make-up are so short-term solutions to border on 'tricking women' (yes, I know that women use those tricks too, I simply would like to invest my time better).
My situation
This is the shortest possible description: I'm a straight male in my thirties, heavily overweight, living in Italy in a 20k people town, with a job paying me about $20k a year.
If you think you need more details ask for them in the comments or PM me.
What I'm already doing/planning to do
The first obvious choice is getting fit, although it's about two years I'm trying different diets with no results, so I'd really need pointers in that direction. I've also heard about training programs that tells you to concentrate on shoulders, because apparently shoulder-to-waist ratio of 1.5 or more is especially attractive.
I've also been told multiple times by multiple sources that women values confidence, competence and leadership. I understand the confidence part in being able to express without embarassment your interest (but still in a socially graceful manner), but I would really like pointers about what area of my life I could engage to become more competent or a leader. In what domains women like competence/leadership?
My only hobby at the moment are the game of Go and dabbing in math/logics/AI, which, as fascinating as they are, are seldom considered very attractive.
What I'm not sure about
Is fashion important? I understand that I need to dress well for my built, but I would like to know if a Versace button down shirt is more attractive than a plain brand one.
False beliefs
Do you think am I doing the right thing? Or am I wrong in my search for attractiveness? Should I concentrate on something totally unrelated? Dose the physical aspect matter or I should concentrate more on character? Am I completely off track?
If you think I'm grossly mistaken, in the name of Omega let me know!
Downvote
If you think this post doesn't belong in a community devoted rationality and self-improvement, feel free to downvote, but at least try to indicate a way to better phrase the problem or point me to another community I can ask the same question.
Thank you very much!