My general opinion is that flood zone buys are great options for buy and hold investors because you can buy at a discount, but rent at a premium (if it's nice).

I'm normally in the opposite situation where i offer a discount to get a highly qualified tenant so i am surprised by this situation. 

Built-in 1976, The Marbella Tower apartment building has only 60 apartments with one bedroom one bathroom with 1,040 SqFt.

The scope of work done was the master bathroom was enlarged to fit a tub.

We had planned to renovate the entire place ourselves.List of violations:properly repair with similar material the broken or defective sheet-rock at east wall inside base cabinets in the kitchen located at apt 2fl, 2nd storyproperly repair with similar material the broken or defective ceramic tiles floor in the bathroom located at apt 2fl, 2nd storyproperly secure the loose base-molding at walls in the 2nd room from north at west located at apt 2fl, 2nd storyproperly repair the broken or defective counterbalance at upper sash south east window in the 2nd room from north at west located at apt 2fl, 2nd storyproperly repair the broken or defective counterbalance at lower sash south window in the kitchen located at apt 2fl, 2nd storyreset, so as to secure a proper and tight connection, the water closet bowl .."

We had planned to renovate the entire place ourselves.List of violations:properly repair with similar material the broken or defective sheet-rock at east wall inside base cabinets in the kitchen located at apt 2fl, 2nd storyproperly repair with similar material the broken or defective ceramic tiles floor in the bathroom located at apt 2fl, 2nd storyproperly secure the loose base-molding at walls in the 2nd room from north at west located at apt 2fl, 2nd storyproperly repair the broken or defective counterbalance at upper sash south east window in the 2nd room from north at west located at apt 2fl, 2nd storyproperly repair the broken or defective counterbalance at lower sash south window in the kitchen located at apt 2fl, 2nd storyreset, so as to secure a proper and tight connection, the water closet bowl .."

Seems like you are already on the right path trying to add a bathroom. 

And if I want to add a bathroom, what should I calculate to plumb that?

I once saw one that was hung in a small bathroom.  

Is this a single home renovation, new construction, upgrades for kitchen or bathroom?