I think also that we probably want to make the sponsorships somewhat exclusive. What I mean is we probably don't want three EDI speakers. It is probably easier to limit it to one from each category.
If we were to limit it by category we'd probably want to first invite back prior year sponsors, then we could do a selective mailing to chosen vendors that we'd like to have as sponsors (based on reputation, etc) then finally if any sponsorships remain we could open it up to any vendors.