I want to build a pistol AR and have the funds to do it but want to make it what I want.

So I want it to be a piston driven pistol with an Adam Arms Kit, is this ok kit ???

Im planning on getting a CMT upper and lower or Voltor

Sig Shooting Brace

Now for barrel I think this is what I want . Gonna be a short range 100 yards and in weapon with Eotech

4150 7.5 or 10 inch barrel 1-7 twist any recommendations ???? I want it short and I want to suppress later on so thinking 7.5 ????
Now crome lined or nitride barrel ?????

Whos a good manufacturer of the barrel I want or you recommend ?

I figure this build is about 1200 with parts except eotech

Finally should I just forgo all this and buy a LWRC or SIG pistol already good to go.

Unless you like alot of muzzle flash dot go with a short 556 barrel.
If you like short barrels build a 6.8spc or 300blk. They were designed for short barrels.

556 needs the barrel lengrh to burn all the powder. All you end up with is a really loud inaccurate gun that produces alot of flash.

Inaccurate?

Only issue in your case with going 7.5" would be finding a suppressor that's warrantied on a barrel that short.  Most only go down tp 10.5"

Inaccurate... no.   I have a 12" barreled pistol with a Sig brace that   I would hold around MOA when i mount a magnified optic on it. As it is I can hold around 3- 4MOA  with open sights or the PRO. I like the 11" - 12" barrels for 5.56, this barrel length retains the most ballistic ammo capability while providing a compact maneuverable package. Only bad thing is that it gets out to around 16" with a can mounted.

I don't know if you want the larger 512 version or a different Eotech... but that looks like a half decent deal.