Good idea with the 3x5 cards!YES to both of your points! We had friends and family write encouraging notes on 3x5 cards at our DS's HS graduation party. I would send a few each week with our letters.
We had the death/illness discussion with our DS before he left. Since we did have a very close call with one of his grandfathers, we knew if he wanted to be told (he didn't - only if it was mom, dad or brother) so we weren't worried about telling him the news until after BCT.
I think we'll have that discussion with my ds and extend it beyond BCT to pre-recognition WRT pets. My long-time beloved cat died during 1st semester of 4 degree year and my parents decided not to tell me until I came home from Christmas. They made the right call. I think I know where my ds stands on family/pet illnesses and death but it would be good for him to make those decisions beforehand.