Given that al your real braking is done on the front, its more a case of whats the max rotor your fork can handle, and you'll get that info from the fork manufacturers site. So most forks 200/203mm is going to be ok. Plus a 4 pot is going to be sufficient, as thats what most are using.
If you are a big fat fatty(like me at about 14+ stone), maybe a 220mm front would be better, but as above thats going to depend on whether or not the fork can take a 220mm
The stock fork is or should be a fox 36 performance, and the max rotor for that is 230mm.
If you want maximum stopping performance, coupled with best cooling, then Hope tech4 E or V4 along with a 220mm vented rotor will be more than enough. MORE THAN ENOUGH, because the vast majority of riders on this site are probably using 200/203mm or 220mm on standard rotors, and more than likely not Hope tech4 V4's, which are I would say in the top 5 brakes out there, and comparable to the basic trickstuff
If you feel that isnt enough, then buy a fucking anchor. Or take up knitting.
All parts of the bike are needed to be able to ride the damn thing, but only the brakes are going to stop you from dying or ending up in a wheelchair, so dont compromise on your own safety. You've spent thousands on the bike, why go cheap on the important stuff.