A series LLC allows for segregation of assets within one entity, though its benefits depend on how well other states recognize and enforce the structure.

Ultimately, it depends on your comfort level with the local regulations and market dynamics.

The idea of debt-free is that if a person is going to retire and has to completely depend on the income, they don't want a severe recession surprising them and causing them to default on the debt and losing the properties.In a normal world, I would do that as well.

I've found hurdles to be of different nature depending on type of project; flipping, new construction or rentals (I've done all three).

I've seen this vary around town between $25 up to $100k depending on the size of the unit. 

Yes but depending on the loan type they may want to understand what that payment is.

I didn't see a minimum DSCR (or Rent to Debt Service), depending on the lender.Because I run my business myself my expenses are little to nothing above and beyond my mortgage and escrow payments. 

don't be afraid of better markets in ohio like columbus. depending on the capital allocation buying old houses and having to renovate is not the only way to drive value. build rent refinance repeat and build to rent are both very strong market drivers as well and you can traditionally get infill land in areas like columbus in much better locations than where you buy.

What documents do they require, what credit scores do they allow, how do they verify previous rental history, etc.?

Whether it makes to sell the rental or keep it depends on your answers to these questions. the property is producing around $855 after property management fee, I have the same tenant for almost 3 years That's a little over $10k/year in cash flow, which is very strong yield for the price.