Here is how you get 100 STR and DEF. I've got it already:
1. Equip Kingdom Key
2. Use Power Ups and Defense Ups on Sora (not Goofy or Donald; Their stats are going to suck regardless....especially Donald; Donald is weak on DEF and STR, Goofy is weak on STR)
3. Go to Neverland; There are Power and Defense Ups in the Clock Tower's doors.
4. Get the postcards; The mailbox gives you Defense and Power Ups
5. Go to the Moogle's Shop; You can synthesize and get as many Power Ups and Defense Ups as long as you have enough items to make them.
Then once you get your STR and DEF to 100 with the Kingdom Key equiped, your stats will be maxed. Now no matter what keyblade you use, you will always have 100 STR and DEF.