Quick answers (opinions) -
1) First lie-flat is MSN 13054, which is about 15 UA frames from now.
2) Yes to 24F on the 73G, but no info has been given about the rest of the NEXT mods. I would assume at least the IFE would be included.
3) 738 will finish in 2026. End of 2027 seems likely for 739 fleet (excepting the non-ER models), but unsure if the 319 fleet will progress quickly. Unsure if the 73G will be finished in 2027.
4) Many were delivered as 175LLs which is the factory-built 70-seat version, but about 1/3rd were 175ERs later converted to LL's. To be more confusing SOME LLs were officially FAA-upgraded to ERs, but others were not. United uses 175SC (SC for scope compliant) for the 70-seat model whether ER or LL version. There is no practical difference between them.
5) SkyWest will grow from 27 to 40 CR5 frames for UAX. GoJet has approximately 7 on "order" which will bring them to 60. Total fleet of 100 as of current plans.