I'm trying to make a game engine with SDL2 at the moment as well, I'm at around about the same stage as you. You're doing good so far, If you want a bit of extra help In seeing how It's all set up, look at the Postal Source Code (It uses SDL2 as well). It's not on the RWS website anymore because the dev's abandoned the open source project but It shouldn't be too hard to find on Github.