I would start out with a fighting rifle to shoot first. A simple A1/A2 upper plastic handguard iron sighted carbine, with a collapsible stock. Get a thin profile pencil barrel. This is the rifle you will actually want to carry if you ever get into a SHTF scenario where you have to sling a rifle for days, because it'll weigh next to nothing, swings easy, etc.
Learn how to shoot it, and see what you don't like about it.
You can then always get a "bling" rifle if you desire.
I don't have a pic of my fighting rifle, but here is my "bling" rifle:

RRA midlength, quad rail, EOtech, flashlight, broom handle, stainless barrel.
It's accurate as hell, but it's heavy. It's probably 3-4
POUNDS heavier than my fighting carbine. Trust me it makes a huge difference.
Many people take the wrong approach to the AR15 platform. They treat the rifle as a toy, buying as many aftermarket parts for it as they can bolt on, and create something that's sure fun at the range, but you'd never take into battle.
Remember why you're doing this. If you want to build a range toy, it's a wide open world. If you want to build something you can rely on if SHTF, build something simple with very little to break, easy to maneuver and carry for a long time, and functional.
Good luck!
BTW, check out AR15.com. They have everything and more you could ever want to know about our evil black rifles.
"Black Rifle Disease makes a heroin addiction seem like a craving for something salty"