Hi Adam,
To convert to 10" wheels you would need to run a Cooper S setup or one of the many 4 pot setups which are available...the standard disc at present will be an 8.4" set up which doesn't fit under a 10" wheel. The S setup has a 7.5" disc...4 pot setups run either a 7.5" disc or a 7.9" disc which fit under most 10" wheels but you would need to check first as some wheels won't fit.
As for lowering the car the shockers have nothing to do with the ride height! in fact if you take the shock off completely the car stays at the same height! To lower the car either cut down the alloy trumpet or the purchase of hi lo's or adjusta ride's is required. Also bear in mind lowering the car effects the camber angle aswell.
Have fun
Oz Cooper
Classic Mini Guru UK