I actually wouldn't recommend a new trigger. It already has some kind of NiB, nickel boron coated, $70-90 trigger group. I put a Geissele on my DMR style build and while it's the tits, I don't shoot 500+ yards enough to really justify it even at Black Friday prices. Putting a free floated handguard on it would probably improve the group size the most bang for the buck. It isn't rocket science, but it can be a pain in the ass to get everything lined up and torqued properly your first time depending on the nut. Buying a vice block or reaction rod makes it much easier. I bet you can find a decent post on how to estimate the barrel nut torque without a torque wrench if you choose some cheap rail popular on reddit. The milspec nut range is like 30-85 ft lbs. Not exactly a precision job.
Putting any kind precision barrel on a non-free floated barrel is retarded. But, I bet he isn't going to buy a precision barrel. He's going to buy some $100 Ballistic Advantage or Rosco that's no better than what's on there. Actual precision barrels are on long backorders and last I checked a $275 Criterion in hand will run you $450 on Gunbroker. I don't even want to know what a Krieger would cost. That's if you can actually find them. Which brings me to another point. There is no reason to build or modify your own upper unless you're doing it for the experience or doing multiple uppers to offset tool cost, and you aren't spending tons of money on expensive components.
Buying a vice block or reaction rod will cost you as much as, more for a nice one, than having a gunsmith put the upper together. Hell, I think Adco is $50+shipping if there is nobody you can trust local. Frank at Compass Lake builds guns for dudes who shoot at Camp Perry, Civilian Marksmanship Program National Trophy Matches, and they'll build an upper for about the same. Paul is going about it completely wrong in modifying that upper and it wouldn't surprise me if he's posting just shit to bait us gunspergs into explaining how to do it right.