If you put a barrel on a rifle that is shorter than 16" you are looking at a "federal pound-me-in-the-ass-prison" offense.
Take the first picture to the left on my last post. It has a 14.5" M4 contoured barrel, but the flash hider is permanently attached by a gunsmith (pinned and welded) to make the barrel at least 16". If you have anything shorter than 16" you technically have a short-barreled rifle. If you want to go that route, start researching NFA regulations.
Everyone starts somewhere. This is the place to ask questions. That is why I built my first one... I wanted something I new inside and out and besides machining the item myself, was MINE, and what I wanted.
Be careful of extra pieces, they turn into more rifles.
In my honest opinion... with brands you will get those who like Chevy's and those who like Fords. If the company has been around for a while they either 1) don't make crap 2) make crap some of the time but stand by their stuff and make it right, or 3) people just keep buying crap from them and don't build rifles with the components. lol
Don't loose your ambition to take on a project. if you hit a brick wall you have joined the right forum, there is many many years of experience here, and even some professionals here that can help bail you out of a bind.