1) Can't help you too much here. I don't have a T-28, and looks like you have most of the +/- figured out. The other consideration is reliability. I've seen all these at the field. The FMS plane's rx was having brownouts probably due to overloading the bec with all those servos. It was also having plenty of nlg (nose landing gear) issues and mlg door sequencing problems. Dynam one seemed OK, I think he might have had nlg issues as well. The legendary PZ T-28, being the simplest, had the least trouble. The only thing I see wrong with those is the canopies falling off. If I ever got one, I'd add magnets to it.
2) Haven't seen it done, but seen their stuff. I'm sceptical about it, but that's just my opinion.
3) The cowl flaps are only eye candy. You understand on a full scale plane those are used for controlling airflow, and therefore, cooling of the engine. The guy having brownouts? I recommended he just unplug those and I think his brownouts stopped.
4) Search the threads out there. Plenty of T-28 stuff mostly involving speeding them up. Haven't seen much about the others, but then i haven't followed the threads on them. Hopefully others who actually own them will chime in and help out.