This is my first car, a tidy 2004 Mini Cooper. I want to upgrade it a bit but not sure what to do, ideas would be appreciated :D

Very nice, i would definatly get some black bonnet stripes on it.

I am thinking of getting red calipers on this car (most likely painting the current ones!), what do you think this will look like?

Yeh I think that will look good. I'd change the side repeater lenses to white though as the red might clash with the orange. I'm not a great fan of bonnet stripes but I don't mind viper stripes. The list is endless as to what modifications you can do but it's an expensive hobby! Another downside is that most modifications would need to be notified to your insurer.