Don't worry about repetition, each person only gets one thank-you note. Compose something that you feel says what you need it to, and modify it as needed. And try to do a few each day so it doesn't overwhelm you. (I wound up doing a chunk of ours at Contata...)

I can't help you with the storage issue, b/c we don't have enough space either. :-) But you can put the cards in a box and tuck it away somewhere, if you have somewhere to tuck it.