^^ got it covered basically. Your shocks will probably be not at their best by then so chucking on some springs isnt the best idea...
if your dampers are on their way out why not try some koni dampers and springs - but the better option would be coils...
you mention money - possibly best to save to cover having to change out the dampers, should that be needed... 18s, springs and old dampers isnt going to be great - will look good mind but not drive well. plus your dampers would then wear even faster with springs on...
possibly best to save to change the suspension properly - springs arent the solution at the moment...
would need to know the wheel offset to see if rubbing may be an issue - i never had rubbing with ET52 and 30mm springs...