You need to be within a limit that are safe and habitable. 

You are not being sold some online course by someone that makes more money selling courses than actually doing deals.

@Kody Smith plenty of good PM software out there but for bookkeeping we recommend QuickBooks Online (QBO).

I have done some online research and few names were referred by many investors.

If long-term rental cash flow won’t cover that debt safely, consider a wholetail/novate to a retail buyer, or sell on terms as the bank (rent-to-own/owner finance) to capture higher price and avoid full gut costs.

—How do you usually determine a safe appraisal gap amount?

Is it legal and "safe", yes.

Quote from @Allan Smith: This seems to be a nebulous topic online, not a lot of info about it other that "you should do it, it's great!"

When properly trained.Is it legal and "safe", yes.

I would store the belongings safely for a reasonable period and follow legal procedures to dispose of the unclaimed property.