It can simplify managing your 20 units and reduce the need for multiple systems.

An ABNB I stayed in last winter was bought the previous year for $525k, that buyer then put it on the market for $525 less than a year after their purchase--today that asking price was reduced to $450!!!

A designer might help you reduce costs and get the property up and running much faster than you could on your own so you have to look at the numbers on a larger scale. 

(But it wasn't apples to apples.)I looked at AirDNA's data recently and don't disagree with their broad picture but again, people here know that the details and other factors can tell a different story and bring success for some in the same area (comparables) and loss for others.I'm all about reducing risk and my read on climate data and global economies (& yes, politics) incline me toward continued investment in properties that have multiple channels of revenue, above a certain latitude, and more upscale.

Don't reduce rent for longer terms.

One strategy could be to make accelerated payments on a 20-25 or 30 year mortgage which can reduce the scheduled payments 6-7 years.

That's how people get over-leveraged and into trouble.If you want to invest, do it the old-fashioned way: increase earnings, reduce expenses, save, then invest.

Also, paying $500 extra reduce the payout period by about 15 years.

I know no one that can help me figure out if combining the two lots will help reduce my property taxes.  

By thoroughly vetting prospective tenants, property owners can reduce the likelihood of problematic tenancies.- Maintaining Property Value: Renting to reliable tenants who pay on time and take care of the property helps maintain its value.