Thief sub is perfectly acceptable for a mnk after level 60. You can trick attack Howling Fist at level 60. Also its fine to use thief sub from 33-50 if you wish. Backhand blow is a fine 1 hit weapon skill that works well with sneak attack. Your backhand blow will actually match or do more damage then a raging fist (41) vs almost all mobs except undead... that is even without sneak attack. Dragon Kick (level 65) will make a lot of mnk want to sub thf because A) It ends level 3 light chain, B) Its a huge damage 1 hit weapon skill.

The white mage sub idea only works if you plan on soloing because you really lack the MP required to truely heal and if you sit to recover mp, you will lose TP. I dont think too many rdm will be willing to refresh you since they already have enough work to do.