Any proficiency with tools would point out that common mechanics tools are all that are really needed for one build.
Here's a link to assembly, note the constant focus on using alternative tools that are commonly available, and how few are really needed:
http://www.ar15.com/forums/t_3_4/22...__GAS_BLOCK___Step_by_step_instructions_.html
When buying parts retail for a build, you pay retail - the makers pay wholesale or less with a volume discount. That is how they can offer guns for less, assembled, to the distributors, who mark them up to retailers, who mark them up again. Yes some are discounting lowers or uppers and you can pin one together avoiding the Federal tax - but it also means not getting a makers warranty FWIW.
Don't focus on Brands - about the only time it makes any difference is when you pick a rollmark on the lower. Lowers and uppers are commodities selling for as low as $40, and a blem is only a blem because it somehow got nicked a day earlier in it's life. If somebody wants to pay a premium to own something completely unblemished for the short time it will last, it's their nickel. Blems don't last long on the markets for a reason - it saves us the effort of tying the rifle to a log chain and dragging it down a dirt road.
Look to materials when choosing parts, there are some things that are minimum standard, and others that are well worth the incremental cost to upgrade. And some things that are sold simply because they can be - the public buys them regardless of the fact they offer no additional value or improvement at all. They are just "cool" and it's all part of the typical male one-upmanship young guys indulge in.
Put your build together with a Range/Target perspective - how far you intend to shoot it, and at what, generally describes the cartridge you want, which determines the barrel length, which sets the gas and what kind of optics and barrel quality. After that, it's all just dress up to a large degree, aside from picking a grip angle that fits the intended use.
The military specifications are considered minimums but they are also compromises and are often negotiated by the contractor. Read them with a grain of salt in that regard. Some features or items are historically known to be pretty lame - the forward assist - so consider whether their inclusion is necessary. However, deviating from military standard usually costs more, as they are low production or custom items, too. Building on a budget sometimes means accepting them when they aren't all that nor contribute to the purpose.
Case in point, the A3 upper with flattop, it's not necessarily the greatest latest to use for a pistol build. Maybe a Gibbz side charger slickside would fit the bill better - if another $150 is in the budget. In my case a kitted A3 for $69 with FA and port cover was just as good.
You get what you pay for.
