It depends on what gear you can count on (will you have trap gear up to date every odd level?), if you plan to use a +2 int tome and the number of skills you want to max.
With a starting int of 8, you can do all the epic traps with the right gear. You can start with 10-12 for more security, especially if this is a 1st character.
Cha doesn't require more than base value. UMD is a class skill so you will have no problem to reach 39.
Try not to put less than 14 Con if possible.