Other benefit on paying extra on one only  is that if/when interest rates drop then better to refinance one mortgage (with higher loan amount) to save cost over two refinances. 

We track most things manually, but use Apartments.com for the units currently occupied (adding more units in our portfolio will incur the Apartments.com premium cost, so I want to explore my options if software is no longer free). 

A house hacker with a  W-2 income can often times float some rehab costs on a duplex through cashflow or supplement some with their income.

People told me I could hire someone to help setup QB for my rentals but this would have cost a couple grand.

Buying for 625K, cost for fix up with 1 ADU about 400K..

We bought the house and the lot at the same closing together from the same source.

The question for seasoned investors is, are mentorships worth their cost, or is doing your own research just as good?  

Expense Deductions: Deduct direct expenses like materials, labor, and selling costs.4.

It simply is not worth the opportunity cost. 

The one month's worth of rent covers some costs (cleaning, readvertising) and the rest is a hedge against vacancy.