You'll actually need 2 switch inputs for each player. Start+Coin

A single U-HID would be able to handle everything, but will require configuring first.
http://www.u-hid.com/home/u_config_utils.phpYou have to tell it which pins will be hooked up to the optical inputs (steering wheels) and analogue inputs (potentiometer in the pedals)
If configuring the U-HID is too intimidating (it shouldn't be), an Opti-Wiz can handle 3 axis; x,y,z(wheel) and shows up as a mouse in windows with no configuring.
One of those would cover all 3 wheels. I don't think GGG offers any interface for analogue inputs, so you'd still need to order an A-PAC from Ultimarc for the pedals.
The A-PAC will show up as an analogue game controller and has enough other inputs to cove your buttons.
It looks like the Opti-Pac sold by Ultimarc only has 2 axis, so if you wanted to order everything from one place, you'd need 2 of those.
You might want to check with Andy to make sure.
Personally I'd go with the U-HID for the sake of having everything on one interface.
If you already know how to wire an optical encoder, you shouldn't have any trouble with any of these interfaces.
If not, there isn't that much to it to learn.
I'm pretty useless when it comes to arcade monitor info, so I got no advice there.