The only completed mods I've known about are the 1965 and 1969. I don't think GPL was designed to be moddable in the same way that Rfactor was from the ground up. I remember someone creating a launcher to select which mod you wanted to use before launching the sim.
Funnily enough I've been thinking of reinstalling GPL as I stumbled across my install disc when sorting throught my stuff the other day.
As for the Microsoft wheel, it should work, but as far as I'm aware you wouldn't get any force feedback.