doesn't say anything about putting the return address on the front of the envelope (that I saw, anyway). Nor did I see a discussion about labels.
Believe me, there is NOTHING WRONG with putting your return address in the usual place (upper left-hand corner).
I think that scotch taping the flap will only call attention to the letter. I wouldn't do it.
Like I said, try to make it look like a business letter. I have been corresponding with my Russian friend for 10-plus years and have never lost a letter in either direction.
FWIW, I also wouldn't ask for a CIS card direct. Their bureau is pretty efficient, and you'll eventually get your cards. I have cards from all but two of the old USSR oblasts (Administrative Districts, like counties) to prove it., and the only reason I'm missing 2 is that the Soviet Union broke up before I could work 'em!)