The only negatives against fiberglass is as temperatures go lower fiberglass looses R value, and the ****** itch factor. On the other hand it can get wet and will dry out eventually. Cellulose's main benefit is it is a fire retardant and does not allow air to circulate within it, thus maintaining high R value. Fire retardant is not needed in this case but stopping air flow within still is a plus, than again cellulose does not do well with leaks, if contained with netting, it will dry but takes a long time, especially in wall cavities.
The vapor barrier may need to be removed as you will need strong netting, taught, before blowing insulation. If the installed insulation bulges out, you will not be able to Sheetrock or any other covering. If your well sealed from possible leaks cellulose is the better insulator. With strong netting and plenty of staples you might get it flat enough that Sheetrock will work with both vapor barrier and netting.
As to the ceiling, use netting, get your covering done ( Sheetrock), then just blow in a decent amount of insulation . Why netting? iF it ever gets wet from a leak you may lose you the covering but not the insulation, it will dry. If not you will lose insulation in area, especially cellulose. Again use cellulose.
You could put up Sheetrock, make multiple 3" hoses in the rock, and blow in the insulation... not a great idea.