I would contact your state DOT for IFTA information.

I'm not sure, but I believe the orginal poster will also need to sign up on the Unified Carrier Registration (UCR) system since he is traveling out of state.  Along with the IFTA, USDOT number and registation for Federal Highway Use Tax (the weight may exempt him from paying on the 2290 - I'm not sure whether he needs to file the 2290).  I do not believe the address is required on the side of the truck any longer - just Co name, vin and USDOT number, but it may vary from state to state.

Being in ag will allow some exemptions but since his stated purpose is to haul the tractors to shows, I believe that automatically kicks him out of any ag exemptions for those trips.  He will probably need to run a logbook, medical card and abide by most, if not all, requirements as if he were for hire.