different size wheels on rear than fronts

[S3SR]

ok firstly is it legal to have 16" on front and 17" on rear?

i ask only cause, ive stuffed a rim, bought 4 BA SR rims still have about 80% tread on front tyres -10% yes past canvas lol, on rears so if i replace the rears with the bigger rims and newish tyres and leave fronts is that ok?
dont care what it looks like, my wallet is more important right now

thanks