IMO the 5 gallon set is the basic set. If you grow yer own, this will do yer trim. If you grow for several people, or commercially, or people 'dump trim at your door', or you grow big crops just for hash making, then the 20 gallon is the way to go. If you are only a casual smoker saving stems and leaves, or a micro/cfl grower, a 1 gallon set will probably do ya.
5 oz X 28g = 140g = 5 batches in a 1 gallon set = 1 batch in the 5 gallon set
Trim variables as to amount = strain, growth conditions, trimming style, green trim or yellow, fan leaves included or not.... too many to nail down to 'you will get X amount of trim from X amount of bud'.
For an example, My bro and I both grow my Sister M, his is leafy as hell, mine is more to the fat nug side, my other friend had it show somewhere inbetween. We all trim differently, and trim amounts vary the same way.