Even a 10% decrease in rent is better than 2 vacant months.

Cash is far too valuable to have it sitting around dead not earning it's keep.Cash sitting in a rental property does not increase cash flow it decreases it.

For example - if the comp house as an additional bathroom, I understand I need to decrease its value to get the value of the house I'm looking at, but do I decrease by 3%, 5%, or 10%?

The value of the business is increased or decreased by the efficiency or lack of efficiency in which it is run.

Once that is completed then you'll show to a HML that you are getting more experienced, which will in turn decrease your rates.

Some states it's 3 years, others it's 5 years, some states pro-rate it each year, and the tenant responsibility decreases as the years of rental goes up.

Write out roles of each partner in a contract.Write out possible penalties if the other party does not hold up their end, such as their profit % is decreased. 

Oh another question is there any other websites like Airbnb to help with decreasing vacancies?

Being that, it’s very hard for me to communicate with my clients and convince them to decrease price or increase their offers.I recently sold a big commercial building in brooklyn and ,thanks god ,deposited a big check.It’s never easy no matter what position you are.

I actively encourage my clients to depreciate as much as possible, since it decreases the tax burden without impacting ability to qualify for additional mortgages.