Here's where I get to show I don't know it all and I'm learning like everyone else.

The key to get the wheels to turn properly will be in giving them the proper name or "tag" and having them linked to the main frame of the vehicle.

I've made meshes for years, but tagging is special to the MS flight sims and I'm still a newbie in that department.  Someone will probably suggest downloading a copy of the makemdl.SDK from Microsoft because it has a list of all the "tags" that work in FS2k2. And it's important to use the exact names that they give.
I don't have the list in front of me now so I'm making these "tags" up, but I want to illustrate a point. If the list says use "c_tire" for the name of the center tire, then make sure you part is labelled c_tire and not tireC or CTR_T because those other tags won't work.

There's a few tutorials floating around here at the simviation site ( I think) but I know there's a bunch over at Felix's site. As a new designer you're allowed to be in both places at the same time  I think Felix has a link to his site in his signature

I have no suggestions as to what kind of gv to make.

I do suggest you do a select all and re-locate the entire shape so the vehicle is lined up with the 0,0,0 point being inline with the front axle. That way the point the vehicle turns around will be in line with the front wheels.
Unless you have one of those new fangled cars where all four wheels turn at the same time, most vehicles follow behind the wheels that are doing the steering.

The 2004 SDK is not yet available and all the old-timers and top-knotch designers as well as people like yourself are eagerly waiting it's release.

There are enough things different between FS2002 and FS2004 that designers will have to pay careful attention to the details. Many FS2002 aircraft have gone into FS2004 without any problems at all. But some had special animations and other "tricks of the trade" and those no longer work in FS2004.