Just a couple of comments...
1. I have found my FX9 extremely reliable. It gets dirty really fast being blowback, but takedown/field strip to clean is an absolute breeze. I clean it every 200 rounds unless I use Syntech ammo, as everything gets fouled up to the point of granular carbon particles that are gritty like sand and adversely affect function.
2. I have a red dot on mine, a Holosun HS515GM. I also have it mated with a Holosun H3MX magnifier
3. For bullet weight, I pretty much ONLY run 147 grain through mine. I have also used 115gr and 124gr but prefer the 147gr for performance (at least for me)
4. Today, at my club, I actually shot 100 rounds of my hollow point HST defensive ammo through it. It ran without issues and accuracy was good at 25 yards
5. Mine came bone dry. Had to G96 the whole thing before using, probably overdoing it
6. I have only used brass cased ammo on it since the manual said to avoid aluminum
7. Additions I have on it are a Streamlight HLX weapon light as well as a Magpul angled foregrip
8. I would suggest a better third party charging handle that is bigger. Mine is a Gen2 FX9 and the "enhanced" charging handle is still way too small.
I have never played with trigger options or buffer weights, so can't comment on any of those
My only two beefs with my FX9 are as follows:
1. Last round bolt hold open does not work reliably/consistently with OEM Glock 17 G5 mags (native 10 rounders)
2. The bolt catch/bolt release goes off by itself for no rhyme or reason. Currently trial and erroring various possible solutions for this