Different approaches suit different people, so mine may not work for you. When I first began looking into getting an AR-15 it reminded me very much of my experience when buying my first computer in the early '80s. Researching that was opening a Pandora's Box of information that overwhelmed me and I just didn't know anybody who could help me out. Same deal many years later with buying a first AR-15.
Eventually, with both the computer and the AR, I decided that I'd never be able to adequately digest all the data that was swirling about until I had some hands on experience and I elected to just buy one of what seemed like a pretty standard configuration just to give me a traction point. In both cases I was a.) glad I did it and b.) discovered something or other that I'd do differently in the future.
You can get yourself started with a 16" flattop carbine with a 1:7 to 1:9 rifling twist from any of the first few tier manufacturers (Colt, LMT, RRA, Bushmaster, Stag, CMMG, Armalite, S&W to name a few that are fairly safe bets) and then learn a bunch about what you may like/dislike/want to add/change. Don't worry about whether or not it has all-weather tactical ashtrays at this point. If it is just a horrible fit for you (unlikely), you can easily sell or trade one of the named brands and move on to something that you'll be better able to decide about. And the Lego-like nature of ARs is such that you can make all sorts of changes to that basic model to fit your desires, once you have a little time on the gun.
Good luck, and come back with pictures!