You can clean Moissanite the same way you would diamond.  As with any fine jewelry item, you would not want to dump all of your jewelry into an ultrasonic cleaner at once to guard against possible chipping, but your Moissanite jewel is perfectly safe under normal ultrasonic cleaning.  Or, for a quick cleaning, gently scrub your moissanite jewelry with a soft toothbrush and a solution of mild dish soap and warm water.

How does Moissanite hold up in repairs and sizing?

Moissanite is a highly stable material.  It is durable and tough, extremely resistant to scratching, abrasion, breaking, or chipping.  In addition, high heat tolerance makes Moissanite less likely to experience heat damage during jewelry repair.