Hi Spencer!
Lots and lots of questions there, so I'll try to help the best I can!!
Basically, the difference between the One, Cooper, and S are the engine outputs. The One and Cooper have the same engine with the One putting out 90bhp and the Cooper 115bhp. The Cooper S has a supercharged version of the same engine putting out 170bhp.
Externally, the One and Cooper are very similar, except the One comes with a black-only hood (roof), whereas on a Cooper you can spec black, blue or green. The one also has a little exhaust tailpipe compared with the Cooper. The Cooper S obviously has the bonnet scoop, different bumpers, side skirts, and a twin rear exit exhaust.
The Italian Job cars were all Coopers (the red one was an S) with the Aero Kit. The thing to remember is, you can always add things on to your MINI - modding is all part of the fun.
Here's a couple of shots of mine, one when new, and a recent one!
Mine is a Cooper, and I've kept the standard bumpers.
This MINI belongs to NickyJ, its a MINI One with the full Aero Kit and the 17" web spokes. Gives you an idea how the Aero Kit can transform the look of the car!
I guess the last question on satnav is one of personal choice. The factory nav is very expensive, and I'm not a fan of the square screen in the round hole solution. I'd save my money and buy a tom tom.
Hope that helps! Any other questions, just shout.
Jon