Yeah, definitely stay away from building your own gun as a way to get started. Especially if it's an armalite. Things don't always line up, excessive wobble etc.
VFC has pretty good internals. HK 416s in general take allot of wobble out of the RAS. No matter what you buy, the internals will eventually break/wear out, and need to be replaced. It's just a matter of how long. I tend to go with best externals as I usually end up replacing most of the internals with performance parts anyways, but I'm good with opening up and trouble shooting my guns.