I'm about to start my first AR9 pistol build. Aero lower, HOPEFULLY a CMMG 5" RDB bolt and barrel, upper TBD. Can anyone recommend a solid LPK with a decent trigger so I don't have to spend $200 on a drop in kit afterwards? And if I can;t get my hands on the RDB kit, what would y'all recommend as a smoother recoiling bolt and buffer system that still maintains last round bolt hold open? Not into short stroking. Thanks.

If you can't get a CMMG delayed blowback, IMO, it's best to buy a dedicated lower from the same manufacturer as the upper.  I've been through the experimentation and there is a lot of frustration and money to be saved by buying a proven product.

Upside is that I now have a spare premium lower and a good start on an AR22 build.

Everybody's idea of decent is different when it comes to triggers.  I bought a PSA MOE+EPT pistol lower build kit mostly because it came with the SBA3 for a buck-fitty.  After I tweaked the hammer spring I can call it decent.  I also went with Endomags, no regrets.  I am running blowback, a 6.5 ounce 9mm buffer with the Faxon 14.9 ounce bolt and I don't find the recoil an issue.  Everybody who shoots it has a smile on their face after.