Changing of bathtub

didn't stick, NOT iron!

when changing the tub, and you will because it's not cast iron, you will have to change the tiles as well. most, if not all tubs, come with a lip that goes up under the first row of tiles on the wall.

as for the leaks, if you're gutting the floor, you can find out. if not, then you'll only find out when the downstair neighbor knocks on the door.

Depending on how the drain piping is installed, you may have to go through the downstairs neighbor's ceiling, so it's worth testing that all the fittings are tight before they replaster that ceiling.

Hofo,

I dont know of anyway there is to"skim" on installing a tub. The last thing a licensed and insured plumber wants to do is install a tub incorrectly. Make sure the gc is using a licensed plumber