Well for pretty much any modding done in BF2, you'll need the latest version of the Battlefield 2 editor. For anything such as modeling, animating, or skinning, it would be a good idea to get the latest version of the PoE plugin for 3ds max.
As for skills just take a look at pretty much anything in the game to give you a reference point. FH2 currently is working on only Normandy, but if there are ever plans to include the early years of WWII, you should definitely send Lightning a pm. He's the military advisor/researcher guy of the team.