I know I should only change the belts when there is some wear. But when is that? 100K is most likely too early but I really don't know what a warn belt looks like. Will there be cracks or discoloring? thanks in advance

 

You wouldn't worry about accessory belts unless it is contaminated with oil. If you want to change them, change them when you do timing belt at 105k as manual suggested. Normally, bad belts would show some signs of cracking.

 

Change them when doing the timing belt.

 

Depends on how they look but if they look good do it all at once at 105k.