I know a few Air Tractor pilots who also have DCS as a hobby and have their preferences, but the most popular models they told me to fly FF here at DCS are the Mosquito and the P47
I also think that both would interact very well with the helicopters on the server.
There are many "civilian" operations that in their basic part coincide with military operations: SAR with CSAR, external loads (there is everything to do here) or FAC with the coordination planes in forest fires or in searches at sea (such as the USCG C130 / C144 Ocean Sentry). I have read further back that they are working on the Marianas scenary. This would be a good place to do sea rescue supported by a fixed wing, such as "missions" where you look for a shipwreck (aircraft task) and be able to launch something as a raft (like oldies B17), be able to mark it on the map where are the wreck and then the helicopters can go to get them out.
Ofcoruse this is a suggestion, I have no idea about computers and I don't know if it is possible, but it would be wonderful to expand operations on the sea and be able to add a couple of propeller planes with the helicopters on this server for joint tasks.
That's why I'm so glad I found this site here at DCS, and best wishes to the server developers, you're amazing guys!