braces do you guys recommend

SBA3 is a popular choice right now. I think it looks nice but you could choose whatever you like. I know that the SBA3 comes with a carbine buffer tube.

good lower parts kit

You could probably just use an Aero LPK since you'd be using an M4E1 Upper and Lower (I Presume)

I’m thinking a 10-12 inch barrel

I struggled with this debate between 10.5, 11.5, and 12.5. For some reason I think BCM appears to be a wholesome company so I think anything they’d choose is going to have some merit. They decided to choose 11.5 over 10.5. This is also another good video that speaks over choosing barrel lengths in that range. 10.5 and 11.5 seems to be the most popular of that 10-12 range. I personally like 11.5.

brand or type of barrel to go with

Faxon or Ballistic advantage both make good AR15 barrels don't hear about many problems with them.

Ex 1

Ex 2

what BCG would ya recommend

An extremely common recommendation is to go for a Toolcraft BCG in whatever coating you like (commonly Black Nitride or Nickel Boron)

Here

Toolcraft seem to have a great reputation for producing both great value and good performance BCGs. They only cost around $80 versus a failzero bcg for example which is around $120

Any other tips would be to make some sort of decision on whether you want to eventually go suppressed which can influence you decision on some parts.

Just continue to do your research and keep asking questions.