spunbearing

Sounds like good advice so far. Only two things that I will add. If you are going to use a fiberglass tub, shovel in a dry mortar mix before you set it to give good support to avoid future cracks. Unsupported fiberglass tubs tend to flex and crack... especially if you have 2 people in the shower. One more note... a common mistake I see in bathroom remodeling is people using greenboard ( moisture resistant sheetrock) on ceilings in bathrooms. Greenboard is NOT approved for use on ceilings unless you have supports 12" on center. If you have any code related questions let me know.