Hi there. Just a thought, but having 4 different tyres of varying tread depth is not going to contribute to a balanced ride!

I had a matched set on mine when I bought it (Pirellis) but they were well worn and it wandered badly and 'tramlined' on white lines and road seams. A new set of Continentals fixed all that (along with 4-wheel tracking) and transformed it completely. If you go for different wheels, you'll still need to buy more tyres, so my advice would simply be to stick new rubber on the std rims. Bear in mind that smaller rims might affect your insurance too, bizarre as it sounds... Good luck.