[JonnyA]

if you have kept within the volvo recommended tyres sizes compatable with your originals the change in wheel diameter will not have (significantly) changed the rolling circumference of the tyre so whether the wheels are 16/17/18/19 or 20" will make no difference to what the car 'sees' when you put the space saver on.

can't make any comment on the brakes, other than why would you need to 'upgrade' them? - volvo brakes have always seemed pretty good too me, subject to being maintained of course.