There are a couple of very good web sites that you can compare different tire/wheel sizes side by side. Usually you can come very close in diameter so if your speedometer is right on now it will not be effected. I upgraded from 14 to 15" and did not have to deal with the speedometer.The best one I have found is

http://www.miata.net/garage/tirecalc.html

As far as brakes, if they fit with the 14's they will fit with anything larger.