Unless you're driving right up to where you're gonna shoot from, and then put 1000 rounds in an hour through your barrel, the extra weight of a 24" bull barrel isn't worth the trade off, to me.
A standard 20" HBAR will be just as accurate, and not weigh a ton in a finished rifle. You lose a hair of muzzle velocity at 400 yards...but how much of your shooting will be at 400 yards, and how much is that 75/100 fps gonna matter? A bull barrel heats up a little slower...but depending on how much shooting you do, the difference isn't that great.
There are so many options, really...just don't think you HAVE to have a 24" or bull barrel to have an accurate critter gun.
I wouldn't pay $160 for a stripped lower...I paid about $80/85 a pop for all my lowers. Granted, I got lucky, since Quantico Arms used to sell Eagle lowers dirt cheap, and I could pick them up in person...but $160 is just too much.
Optics are more important for the kind of gun you want to build...you're much better off building a relatively standard rifle with a really good higher X scope, imho.
I've got an ER shaw barrel from Model 1 that outshoots either of the OLY SUM barrels I have...and they were twice the price.
What I'd recommend:
Ameetec or Mega Lower (stripped) Ameetec has some other brands, that are cheaper...you might check those out, as long as they're forged.
RRA or CMT A4 upper (complete) Don't get a raised platform, they're not really necessary...a set of high rings will give you all the scope clearance you need.
20" ER Shaw barrel OR 24" fluted ER Shaw Barrel
Yankee Hill Lightweight rifle lengh float tube (that's the four railed one)
RRA Bolt/Carrier assembly and charging handle.
RRA lower parts kit
YHM low profile/specter or railed gas block
Buttstock of choice...I like the fixed A1 length VLTOR, buy ymmv. Using the stock buttstock for a while save you around $100 that you can put into the scope.
Harris bipod...either of the 2 short ones, but you need to weight bench rest length vs. something a little taller.
The infamous "15 minute trigger job" would *probably* get the trigger fairly nice, just be careful during the polishing stage. If not, add another $120 or so for a good two stage trigger.
For optics:
Weaver Grand Slam 6x20x40.
If that breaks the bank, then go for a Meuller or Swift...they'll be $100 or more cheaper for the same kind of magnification.
You should be able to do all that for around $900, minus the trigger and an exotic buttstock...you can always add those later after you see how it shoot. I'm sure the rifle would do anything you needed it too, AND not need its own set of wheels
Given that you like to tinker with stuff, you'll probably be changing stuff before too long...but the basic rifle will be solid, and get the job done 'til you start swapping stuff around every week like I do.
Get yourself an action block and an armorer's wrench, and you're off to the races.
This pic is less than 2 months old, and the only one that's unchanged is the tan one...that A2 upper just stops me cold in my tracks hehe.