Amen to the cartridge trigger. It is as tempting as the Original Apple and leads us down the path of poverty.
Pardon my ignorance(or don't), is a buffer tube and spring still needed for one of those builds?
no, at least on the CMMG/RTB bolts the recoil spring rides in the charging handle channel in the upper, the rear end of it has a tab that sits against the upper face of the buffer tube tang, that is basically what takes the recoil force, and holds it in place, can eave the buffer/tube/spring/retainer out if you wish. Can also run things like the pic rail adapter to use a Sig style folder being you don't even need a tube on dedicated 22s. The gap is also something to keep an eye on if the bolt assembly is loose in the upper or if it won't close all the way.