So my two teens and I recently decided to resell one house because after doing the demo and looking at what we have to do to fix it, none of the things are the things we actually enjoy doing. 

In your case you need to demo the existing wall and tub.

You can underpin or demo and rebuild but either option may become expensive. 

If you are near me, I'll give a demo ride... after you pay for lunch at Crazy Fire in Raleigh;) 

If I had a house next to a sewer plant I could probably demo the sewer plant if I bought the city a new one somewhere else, or I could salvage the house by having it moved to another lot.

House is mostly plaster and lathe, top floor demo is complete and ready for new framing.

Super excited to see you've started demo on the property already!

Do all your demo work first and at the same time get on the phone and start booking your subcontractors (windows, doors, siding, roofing, electrical, HVAC, plumbing, etc.)...they will likely (if they are good) have a long lead time so you can do any small tasks in between their availability...don't remove your old flooring until you've painted that way you don't have to cover up the floors...just spray and drip at will.

oh and the best part is we were about a dumpster full of demo along in the house that I don't really own!

He has a rehab valuator Lite that you can download as a free demo.