General rule for dividing and repotting is to leave at least 3 bulbs together. Can be one 'Back Bulb (those that look dormant)' and two green ones. As far as removing the Back Bulbs, I remove a few but be sure to leave one or two as these supply food for flowering. Say there are 4-5 Back Bulbsd and 6 green bulbs. I'd divide the plant in two with 3-4 bulbs on each and then remove 2-3 of the back bulbs. You can germinate the back bulbs with a fair amount of success. I take presoaked bark (only bark) and fill a quart ziploc about 1/3 with the moistened bark. Then take the cleaned back bulb that has dried for a few days (be sure to be careful of any eyes on the base of the bulbs) and bury them 1/3 of the way in the bark. Seal the ziploc. Let sit for a few months in a place with indirect light. When they germinate pot them up. As always when repotting remove any rotten roots. I usually cut the roots half off to make dividing easier. They will regrow. Also remove dead matter from the sides of the back bulbs if you can. Scale can live there so it's good to inspect.