Here is a link that describes about the payouts for posts in great detail. https://steemit.com/tutorial/@ilyastarar/understanding-steemit-know-how-steemit-reward-system-works-and-how-rewards-are-distributed

As far as where does the money come from, just like Bitcoin, new coins are being created every day. I believe Steem is at 9.5% inflation and goes down 1/2% every year until it reaches 1% inflation. These coins, along with ones received by Steemit from advertising within Steemit are used to create the reward pool.

I think eventually everyone will be here, some lose interest because they think it is a get rich quick scheme and it isnt. If you are a content creator though, it only makes sense to me to create it where you can make $ off it and then share it on your normal platforms.

I describe steemit as reddit, instagram, facebook and twitter rolled into one, and since no one owns the site, the value is retained by the content creators instead of the middlemen hosting the site.

The more Steem you power up, the more your upvotes are worth(and you can vote for yourself), this makes sense, as the more money you invest in the platform, the better steward of the ship you should be.