Lots of good posts.
First off, I'm glad that your planning on using the Innovation First controller. In terms of simplicity, it is ideal. However, there are some limitations.
Check the quality of the 12v coming out of the car. I'm not terribly sure, but I recall that auto electrical power is usally not very 'clean'. I don't know what the RC can handle in terms of voltage variation or current. Just hook a multimeter up to what ever you plan on drawing 12v from, and see if it spikes or is high or low or what not. It probably won't be a problem, but...
This was mentioned before, but I think it deserves some further mention. Radio contact is always something of an issue. The range on the link is like that of a older portable phone (the 900mhz variety). For the purposes of FIRST, its more then enough, since the bot is never more then 50 feet away and in direct line of sight. Your project may not be in such ideal conditions. I've noticed that on older radios, random packet loss and interference can be a problem.
When the RC loses radio contact, all it's outputs will go to null. That means no motors will get power and relays will open. That's great for FIRST, since the 'bot for all intents and purposes can't hurt anyone in this state. This car however, will probably stay in drive, and will probably keep rolling along.
I would strongly suggest a deadman switch, that will turn the car off (or stop it) should you lose contact. I can think of a few ways to do this with the RC, but I'm sure you can come up with something.
Perhaps some sort of speed limiter to? Say something breaks, and the car flys off with the pedal floored. Maybe a little limit switch on the throttle cable or a optical sensor on the speedometer that would see the needle pass 15mph and activate that kill switch. Heck, why not just hook the speedo cable up to some sort of tach and report back the speed to the operator interface? Innovation First has a wonderful dashbored program that lets you view feedback from the RC. Some serious brownie points there, if your up to it.
Yesh... I should unplug my keybored now to shut my self up. Have fun, this sounds like a cool project. Just make sure the parking lot is empty when you go test this thing
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-Andy A.