Creating jobs doesn't look to me like a task for a startup. Every startup that works automatically creates good jobs.

With luck, marijuana legalization will give people a less harmful and cheaper way of escaping from reality for a bit.

The evidence doesn't suggest that marijuana legalization increases consumption.

Mine will deposit a check if I take a picture of it in their app, but that requires an expensive smartphone.

You get an Android smartphone for 29.99$. When the iPhone was introduced it was expensive but as technology progresses yesterday's inventions get cheap and accessible to more people.

I'd have to look up some figures to double check, but generally speaking cities get a disproportionately large amount of tax revenue pumped into them.

Not in contrast to the tax revenue they raise. More government money get's transferred from cities to rural parts then the other way around.

However, a priori it seems like cities don't have any resources, while in the country there's no shortage of rocks for concrete or timber for construction

Shipping rocks around is cheap. Inventing new ways of doing things with rocks is more important for generating new jobs and it's generally done in cities where people with different ideas and skills congregate.