If the timing belt breaks - and trust me, after 100k miles, it's been weakened or at least stretched - you can get the old "oops my valve hit the piston" problem
not good. Even if it's stretched, you can get some weird symptoms like backfiring up the intake, reduced power, etc, depending on its condition. Definitely get it replaced.
Other things to look at are the O2 sensors, catalytic converters, U-joints, change tranny fluid (which should be done every 30k miles if you can), shocks...at 100k, there's a lot of stuff that warrants a look. Basically, if it moves a lot or takes a lot of stress, it should be looked at, and replaced if needed, but the stuff listed above would be at the top of my list.
As for brakes, IMHO you'd get more bang for your buck getting good brake pads than performance rotors. The slotted rotors will help under hard, extreme use, but for a daily driver, all they really do for you is look pretty. A good set of pads, on the other hand, can both reduce the amount of brake dust you have to clean up, as well as bite the rotors harder, giving you more stopping power.