Also, is an invoice from this person enough a record for tax purposes or do we need a receipt of a payment from him?

Below is a snapshot of recorded documents from one (note #1) of the many investors who got slammed by the GR and FC.

Better safe than sorry.Changing the number of baths and square footage is going to be an easy thing to spot when it doesn't match what's recorded at the appraisal district. 

While there's always a chance of short-term depreciation, historically, real estate has a strong track record of appreciating over time.Vacancies and Maintenance:Vacancies and maintenance are part of being a landlord, but there are strategies to mitigate them.

You can also find a helpful realtor to research the data through the mls or a public records database.

They won't pay, but I'd take them to small claims court anyway, to get it on their record.

In Maryland there is a law if it is not recorded the borrower at any point can request all payments be reimbursed back to them.

At the time the property is sold or refinanced the quit claim deed could then be recorded. 

Or the same can be said about a group going public with a great track record for their successful IPO.  

If it is on one tax lot, it would be recorded as one property on your schedule E.