Well I can confirm you can go full time hive. I live in one of the richest countries that costs a small fortune to live in monthly and I work 100% hive.
There's one avenue you haven't factored in yet. Build a business here. Get a few devs that you might know that will help and build something cool :)
Yes, you are quite right. I chose to specifically focus only on author rewards, aside from simplifying the analysis but because it's the most straightforward, lowest barrier to entry method of earning here, and will likely always represent the largest population of earning/economically active users on Hive.
Good point. Also, if you're that way inclined then I think building a business is the natural flow of things.