[Zeke]

I doubt the thermal camera will do much other than you say and they aren't a bad thing. I just wouldn't spend a lot of money. It won't show vents for instance. Electrical is easy to find. Plumbing is pretty easy looking at vents at the roof, clean outs, ect.

Do you have a permit for this. You mention floor sinks. Each counts 2 plumbing units IIRC and over a certain amount of units you need a 6" main.

The questions you ask are telling me you have no idea. Wait until you face ADA. That will change the picture dramatically.