It's money you set aside to replace items that have shorter lives than the property itself.

You'll have to have a larger downpayment: 25%, usually a higher interest rate, and often but not always a shorter lending period: 20yrs is frequent. 

These typically require more down, have higher interest rates, and shorter loan terms (typically up to 20 years instead of 30).

But as a risk mitigation strategy in the shorter term for future eviction moratoriums, high unemployment and other (landlord) unfavorable politcal or economic policies, we are planning to make a big effort to find section 8 tenants for maybe 10-20% of our units.

If you want an even shorter one - Unless your personal net worth is over 500K (Don't include your 401K), I would recommend just keeping it in your personal name for simplicity's sake. 

Houses there are cheaper and rent can be higher for shorter term rentals.

With a shorter seasoning period with commercial loans or flips then they're doing even better.

On one hand you could do a shorter term rental in which case keeping it fully furnished wouldn't be a bad idea.

Will it mathematically be better to own multiple properties with 30 years terms and pay much more interest or shorter terms with less properties?  

I know you will be able to get a really good handle on how the process works and what you need to do in a lot shorter time than it took you to earn the money you are getting ready to invest, so spend the time to educate your self don't just trust that what is being told to you is accurate.