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Need
Barrel nut - Need suggestions. Preferably a black nitride, strong, branded barrel nut. If you use the M5E1 upper it uses a proprietary barrel nut for it's proprietary rail.
Gas Block - Does Geiselle make .308 gas blocks? Standard diameter ar15 gas blocks fit, the model will depend on the contour of the barrel you choose.
Gas Tube - Guessing these are generic depending on length, rifle length gas tube I am assuming? I am looking for a 18-18.5' barrel. There are two rifle length tubes, most follow the DPMS pattern that uses AR15 tubes.  Armalite uses a longer tube for rifle length gas systems and mounts their gas block about .5" farter down the barrel on rifle systems.
Trigger - American Trigger Gold Flat Trigger .308 variation (are triggers interchangeable in between 223 and 308?) Today most AR10 variants are designed to use AR15 pattern triggers, occasionally their are issues like PSA lowers not working with Geissele triggers without some modification to the hammer.
Muzzle - MOD FSC30 OR Fortis Rev Brake 7.62 Most 7.62 or 308 breaks are threaded 5/8x24, just make sure the threads are the same between your barrel and muzzle device.
Buttstock - Magpul PRS Adj  vs MBA1 http://www.luth-ar.com/product-category/buttstocks/mba-1/ DPMS and Armalite use standard AR15 buttstocks, a shortened rifle buffer tube and a similar rifle buffer spring.  Armalite uses the same spring between rifle and carbine applications.  DPMS uses a special shortened buffer and buffer spring in carbine applications.  DPMS uses AR15 carbine buffer tubes while Armalite uses a lengthened buffer tube for their carbines. I like the PRS better than the MBA.
BCG - Have not looked at any yet, need recommendations, digging the Gold F1 Firearms 308/7.62 BCG JP high pressure bolts are the best. Just make sure your bolt and bolt carrier come from the same company.  If you get a Krieger barrel, you will pull the bolt down and send it to them, then they will headspace your custom barrel to it.
Buffer+Spring - Are these interchangeable? If they are I'm thinking of getting the Damage Industries H6 again or Geiselle's Buffer, Spring kit. You need a buffer tube, spring and buffer that all match your chosen butt stock. I like Sprinco springs. Geiselle's kit probably wouldn't work very well. You could use an H6 if you were using an armalite carbine tube, but I think the stocks you have listed both use rifle buffer tubes. 
Upper/Lower Receiver - I want to go with Aero Precision's M5E1  because I really like the design and they are cheap, hopefully good quality!  I like my Aero M5's, I haven't used the M5E1's but they are for use with the specialized Aero rail and barrel nut system.  Personally I would go standard Aero M5 and then pick a rail that matches the M5's DPMS high pattern upper rail (.210 rail height). 
Rail - Rainier Arms Switch Rail hFortis Rev Switch rail too, but I like the cut by the muzzle on the Rainier's. This won't work with the M5E1 but would work with the M5.  SLR has a lot of nice rails for .308's as well.  Generally I'm a little budget minded so I use Midwest Industries 15" Mlok rails on my M5's.
Charging Handle - AXTS 7.62 I like these.
Barrel - Here is the part where I am most confused about, I am looking into Krieger, Criterion or Noveske. I want a 18-18.5' barrel, I have no idea how to order through Krieger, its hard to find a Noveske Krieger has a form you fill out then they contact you to make sure it's what you wanted.  Delivery can take several months but they make great barrels.
Iron sights - KAC Micro BUIS

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You might just get a barrel and BCG from JP.  They have excellent barrels.

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Need
Rainier Arms SWITCH KeyMod .308 Rail 14" https://www.rainierarms.com/rainier-arms-switch-308-rail-14
PRS® Precision-Adjustable Stock SR25/M110 or MBA1 http://www.luth-ar.com/product-category/buttstocks/mba-1/
Geiselle SD-E https://geissele.com/super-dynamic-enhanced-trigger.html
Aero Precision's M5E1 Upper Receiver http://www.avantlink.com/click.php?tt=cl&pw=55963&ctc=ix1e56wuuo00zk8a02gtd&mi=13601&url=http%3A%2F%2Faeroprecisionusa.com%2Fm5-receiver-set.html Technically this is an M5 receiver not an M5E1.  It's the correct model you need for the Rainier Arms Switch rail you listed above.
Aero Precision's M5E1 Lower Receiver http://www.avantlink.com/click.php?tt=cl&pw=55963&ctc=ix1e56wuuo00zk8a02gtd&mi=13601&url=http%3A%2F%2Faeroprecisionusa.com%2Fm5-receiver-set.html
AXTS 7.62 Charging Handle https://radianweapons.com/catalog/product/view/id/57/category/4/
MOD FSC30 https://primaryweapons.com/store/product/flash-suppressing-compensator/ or Fortis Rev Brake 7.62 http://fortismfg.com/ar10-fortis-red-brake-762-nitride-rapid-engagement-device
JP Barrel http://jprifles.com/buy.php?item=JPSM308-18L11R
JP BCG http://jprifles.com/buy.php?item=JPBC-5AHP#

Still looking
Barrel nut - ? The Fortis/Rainier Switch rail comes with the barrel nut you need.
Gas Block - Geissele Super Gas Block (Nitride Black)
Gas Tube - Rainier Rifle Length Gas Tube
Muzzle - MOD FSC30 or Fortis Rev Brake 7.62
Buttstock - Magpul PRS Adj  or Luth-AR MBA1
Buffer+Spring - ? I like the Armalite 308 rifle buffer and Sprinco Red spring.
Iron sights - KAC Micro BUIS

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jaqufrost you are the best! Thank you so much, I wanted to get Krieger but sending them parts and what not seem like a hassle especially if it takes a couple of months, any other recommendations?

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Sorry I tried. Maybe give them a call and see when they expect more in stock?

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Krieger headspaces their barrels for std. USGI bolts. No worries there.

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Hard to do much more than speculate at this point with the holiday and businesses closed and unable to take calls on technical questions. Not sure if Krieger headspaces all DPMS style barrels the same, but my barrels all headspaced to JP HP bolts.

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What barrel do you use?

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I thought I'd mentioned it previously but I must be thinking of another thread. I bought one Krieger from Fulton in 6.5CM which is istalled in an upper, and two more 6.5CM barrels from Krieger direct that are uninstalled replacement barrels. All are 22" and .936 at the gas block and all are headspaced to different JP HP bolts.

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That one won't work, any of these barrels should work.
http://www.fulton-armory.com/far-308-barrels.aspx