Down to the studs, raised the ceiling, added a toilet room, nice, but not "luxury" finishes. 

If we have a vacant house whether rental or rehab in the winter, we usually winterize the houses by draining all the water and heating system, blowing out the line with compressed air and using RV antifreeze in the traps and toilets. 

I don't point in on the wall toilet paper holders. 

I am  plumber from massachusetts as far as things to discuss with the plumber go just make sure you give him a solid time frame that is agreed upon by both parties and make sure you know the answers to his questions. for example finish work like what kind of faucets, what color toilet etc. the little things is what slow the process down.

I was talking with a friend who said they had a $500 water bill from a running toilet.

I was quoted $5k for the shower+vanity+toilet - Plaster and paint for entire unit is $6kWould you hire one contractor to do it all or do I hire different companies for each item?

While trying to repair the damage (new tiles, new toilet, new vanity, new door, new cement board, etc.), how should we work with our tenants?

After selling RE for 10 years or so ( specializing in land and land development) I mentored with a HML in Oakland and ended up Running the company and an equity stake.. 89 hit ( earth quake War ) and Norther Ca RE went into the toilet.. had to pivot.. got into Timber and land in Oregon and did that through the 90s Loved that bizz until log market soften a bunch and a lot of consolidated mills etc and the business for us kind of died down..

The 1/2 bath going in the basement was no exception to the compromise I mentioned; it cost more for a macerating toilet, ate up valuable finished basement space and doesn't make quite as much sense as a 1/2 bath on the first floor for company.Even the labor is a compromise.

I like to take 20% of my monthly rent and put that aside for vacancies, roof, boiler, toilet, anything that can go wrong.