In the keeper league I run, keeper cost is paid by draft picks including additional loss of draft picks for top 70 players (luxury tax). We cut to 10 players right after season, then to 5 or 6 (optional) come the spring.
In the offseason, trading of any draft picks are allowed but we avoid potential problems by:
1. Not allowing picks for picks -far too hard to evaluate in a way that leaves everyone happy. I cna easily come up with a value system for it but its just too intangible so IMO its best to avoid
2. So many of your draft picks get blocked by cost to keep that many of the better performing teams the past year do not have available good picks to use to improve, where the lesser teams generally do
3. If you trade for a player he LOCKS into your keepers with an injury exception if deemed "seriously hurt" this way no one is firing off too many draft picks for players they wont keep or in general going too crazy with it
4. We dont allow in season trading of picks, because in theory in our system no one is 100% sure what draft picks they will have available until the offseason. You could do this though if you wanted I would just suggest to ahve anyone prepay in full for future year(s) if they dip into picks.
"I'm the man with the ball. I'm the man who can throw it faster than F***. So that's why I'm better than anyone in the world." - Kenny Powers