Hi Everyone! First post on the site. I recently bought this lower receiver with the intent of building a quality AR.
http://www.avantlink.com/click.php?tt=cl&pw=55963&ctc=j0rgxz2lil00zk8a00y51&mi=10077&url=http%3A%2F%2Fwww.brownells.com%2Fuserdocs%2Fproducts%2Fp_953000018_3.jpg
Brownells
So far my thought process is to go with .223 Wylde. I like the idea of having some flexibility between .223 and 5.56 with good precision. Aero has a complete upper in .223 Wylde for $475
http://www.avantlink.com/click.php?tt=cl&pw=55963&ctc=j0rgxz517800zk8a02gtd&mi=13601&url=https%3A%2F%2Faeroprecisionusa.com%2Fmedia%2Fcatalog%2Fproduct%2Fcache%2F1%2Fimage%2F9df78eab33525d08d6e5fb8d27136e95%2F2%2F2%2F223-wylde-18in-gen2-complete-uppers.jpg
So i have a few questions for you folks.

1: Any recommendations on a BCG and lower parts kit?

2: Keymod or M-lok? (I know this is like asking "AR or AK" but i hope you guys have some knowledge about what is receiving better support in the shooting community)

3: 16" or 18" barrel? (So far I am leaning towards the 18")

Thanks guys!

1: Any recommendations on a BCG and lower parts kit?

For LPK I like buying from Red Barn Armory because you get to pick all the parts grip, trigger, safety, trigger guard, etc..
BCGs from Aim Surplus are good either V2 or Nickel Boron.

2: Keymod or M-lok? (I know this is like asking "AR or AK" but i hope you guys have some knowledge about what is receiving better support in the shooting community)

I have both keymod and M-Lok. Seems like more accessories for m-lol but is completely opinion only.

3: 16" or 18" barrel? (So far I am leaning towards the 18")

I like 16" barrels just to keep the OAL and weight down. My rifles can put shoot me.

Thank you! Trying to do my due diligence before buying parts. Can you explain the V2 vs Nickel Boron? Is one less prone to build up or something like that?

- Joe

The AIM V2 is nitride and the other is Nickle Boron.  Advantages are that they can be smoother and easier to clean than the standard phosphate BCG.  One of my rifles has a standard bolt carrier with a Nickle Teflon plated bolt (supposed to be even slicker than nickle boron).  It works great, but I still have to clean carbon deposits off of the bolt with a brush.  In my experience they don't just wipe off with a rag like some claim.  Another good source for quality BCG's is Toolcraft or their Cryptic Coatings branch for high performance coatings.