Seems to me you might be violating your "keep it simple" rule by having that "bonus" keeper.
If I were you, I really would keep it simple for the first year.....just have 3 keepers, period.
As far as dealing with "dump trades" go, my advice is don't deal with them...just let them happen. IMO dump trades are part of what keeper leagues are all about.. Personally, I play every year to win, but when I know that's not going to happen, I don't have a problem with playing/trading for next year.