In this case, more is better, and it is really hard to overdo ventilation. Ideally, you would use a fumehood for iodine. That said, a well made box that seals with ground glass and/or Teflon should hold most of the iodine fumes and you can probably get away with a well vented darkroom. By well vented I don’t mean the bathroom fan that most folks seem to think is adequate, but a real vent that does more than make noise.
The problem however is that with darkroom ventilation you will need to open your box elsewhere if you want to add or just admire your iodine.
My advice? Buy or build a fume hood.