Moving Plumbing in Slab in Florida

We are about to embark upon remodeling the tiny master bathroom of our 1962 Florida home. We currently have a single sink, toilet and 36 x 48 shower all in a row. We plan to take space from an adjoining closet and utility room to add a tub, move the toilet and make a double vanity. The existing space is 8.5 x 5. The new space will be 10 x 10.

The shower is staying in the same place (but the door will be moved, thus the faucet/head need to be moved). The tub is going to be placed where the toilet is, but the drain needs to be moved approximately 18" (in line).

The toilet is going to be placed directly across from the shower door opening. The washer / dryer will be in a wall behind the toilet.

The house was replumbed a few years ago, so all the supply lines are in the ceiling/roof crawl space, and very easily accessible.

There will need to be new lines from the existing plumbing just above to all the new fixtures. The plumber wants to add a new 3" vent behind the new toilet placement, and remove all the old 2" cast iron vent through the roof.

The plumber estimated he will need to break a trough about 2 feet by 1 foot to extend the current toilet drain for the new tub drain, and at most about 5 x 4 to expose all the rest of the existing drains/sewers, tap into them and make all the new connections. He will be resetting the concrete.

All the walls will be open, down to studs. The plumber is only doing concrete cutting and work. He estimates he will take 2 days for the rough-in, then come back to help set the tub, and then 1 day for installing faucets for the tub, shower, & sinks, and the toilet.

I have a $10778 estimate. It seemed a little high.

Questions?
1. can he tie the new fixtures into the old cast iron vent through the roof, or should it really be a 3" vent through the roof, considering the addition of a tub?

2. Should I seek a few more estimates?

There is no code requirement for a 3" vent in Florida anymore. That being said, I'd call for a 3" vent for those fixtures, it may be slight overkill but only slightly. If for some reason all the drains were in use at one time you would need a 3"....for just a couple of fixtures the 2" would work fine. For the washing machine trap you'll need a 3" up to the trap tee....so you're gonna need the wall space for a 3" pipe anyway.

Can't help you on the estimate...I only draw plumbing, I never install it. You should at least get two more estimates anyway.

Good luck with your project.