I'm not trying to offend anyone here, but ARs are not difficult to build. Sure, when I checked into MOS school, I thought it was an extremely complex weapon. 2 hours later I realized it's not.
Tools are not that bad. You only need a barrel wrench/multi-tool which you can get for about $20. You can grab punches for dirt cheap at Harbor Freight, or buy just the sizes you need, you need only to clamp the barrel in the vice, with aluminum jaws, or you can get the plastic upper kit if you'd like.
The torque wrench, I honestly have to say I used about 3 times out of the 300 barrel changes and 200 upper changes I did. You'll know when it's tight enough, the specs are between 35-85 ft-lbs, don't quote me on that, and you're really trying to just line up the nut for gas tube, while having the barrel tight on the upper, thats all.
I've assembled lowers with a carpenter's hammer, big screw driver, and some rubber matting, thats it!. Plenty of masking tape will protect the finish of your lower when you start driving pins into place.
When building an AR, it seems cheaper (total price) to buy a complete upper, less barrel (with forward assist and ejection port cover) already installed. After finding the upper kit, that's in stock, and after paying shipping, it comes out to break even, or maybe saves you a few cents.
If more than 2 guys are gonna build ARs, I suggest you share headspace gages. You only need them every so often, depending on how many rounds you're throwing down range. If I built a brand new gun with new bolt and barrel, I'd bet it's 99.99% safe, and I'd shoot the first round through it. Headspacing is a MUST if you are using a used part kit (for AKs, FALs, etc). But with brand new barrels and bolts, you should be good without it.
In the Marine Corps, I was an armorer, and have personally fixed over 5,000 M16s in the past 4 years.
PM me if you wanna know more about ARs. I am coming home from the Marine Corps to MA within 3 weeks.
I'll be job/school searching, so I will have plenty of time on my hands. To get around the transfer of weapons/need for an FFL, if I said you buy the lower, I'll help you find the parts, and you could come to my garage and build an AR with tools that I have, would that be a reasonable offer? Your lower will transform into a full AR with the supervision of myself.