1) Any frontend that works with a gamepad should work with a steering wheel.
I haven't seen one that scrolls horizontally though.

Mbasile is getting close by tweaking Hyperspin:
http://forum.arcadecontrols.com/index.php?topic=114400.msg1223406#msg12234062) Depends on how you are going to go about the conversion.
Hacking a pc wheel or buying an interface (which would forgo ffb)?
Sticking with the arcade monitor or swapping in a TV?
3) I think Gbeef's cab started out as a Sega Rally, but there's not much left of it.

See the examples listed in the Driving Cab Thread linked to in my sig.
If you're knowledgeable about electronics, consider doing this hack to interface the controls.
http://translate.google.com/translate?hl=en&ie=UTF8&prev=_t&rurl=translate.google.com&sl=fr&tl=en&twu=1&u=http://www.gamoover.net/tuto/l2m2-interfacer-un-ffb-et-volant-sega-model-12-avec-un-pc-ou-une-playstation-23I'm told by people who have tried everything that it is the most true to the original arcade feel.
(It will only work with the original Sega Rally controls. If it's Sega Rally 2, it won't work)
Set up your software first to make sure that you'll be able to play the games you want. Driving cabs are a PITA to set up.
Just getting the various emulators to launch and go fullscreen takes a lot of trial and error, regardless of front-end.
You'll end up running 5 or 6 emulators just to get 40 or 50 arcade games that play well.

After you have your list, the controls for every game must be set up and tweaked individually to get them to feel right.
Do you already have a PC? If not, what were you thinking about getting?
It takes some serious power to run Supermodel and the newer 3D games in MAME.
There's been a lot of improvement to Ridge Racer, Ace Driver, and some of the Gaelco games in MAME recently.
They run beautifully, but it takes a beast to run them full speed. (my driving cab can't)