What should I expect in terms of premium for $500k coverage?

How much insurance coverage do you have and does your policy even cover a dog large enough to jump a six foot fence?

It will likely depend more on the property's debt service coverage ratio than on an arbitrary percentage. 

I am going to supplement the wood floor in a few spots with vinyl glue down planks.

If the terms of the mortgages were refinanced into 30 year AM (amortization) the P&I (principle and interest) payments would appear much lower and hence the resulting cash flow would be much higher when they (lenders) go to calculate your cashflow for DTI or debt service coverage purposes.This also could be an issue with how you file your tax returns for all of these 15 doors or a combination of the above.Either way its really easy to fix.

I'm not looking to get rich quick, just to build a real estate portfolio to supplement my military income so I can retire at a young age.

Don't rely on your GC's coverage for losses.

Tenants don't want to deploy property protection and so I always get loss of use coverage so what repairs are needed you can recoup some the lost rents.I've heard people like the panhandle but I'm not familiar myself.

Some general guidelines:No foreclosuresNo bankruptciesNet worth > loan amountLiquidity > 9-12 months of P&IDSC > 1.25 (debt service coverage)Experience in the asset classThese vary by lender, borrower, and property.

I guess you could develop a second cleaner-helper-handyman as backup.There is an insurance coverage issue that I don't worry about because I have umbrella policy, but you might.