This is newbie talk, so don't kill me. I want to learn, but it seems so complicated.
I want to - sell BTC for ETH, and then sell that ETH for more BTC than I started the trade with. Sounds like a simple way to start, yet I know it won't be.
My biggest concern is that there are so many exchanges. How the heck do I know which ones will pay me after I make an exchange? I know I have to check their reserve balance, but what else should I look for?
I can see that you are very interested in trading your Bitcoin for Ethereum but you are skeptical whether you are going to get what you will apply for or not. Well there are good exchanges out there from centralized ones to decentralized ones. Since you intend to trade your Bitcoin for Ethereum and you are not really for the headaches from exchanges, you can make use of individual exchanges here on the forum. We have reputable members here that can accept your Bitcoin and give your Ethereum based on escrow.
If you insist on using an exchange then you can use exchange like Binance and it there exchanges. Although Binance is centralized so you will have to prepare for KYC cause it's very necessary using the exchange.