How to Calculate the OPTIMUM amount to pull in a refinance?

[Alfonso Montejano]

I own a couple properties that have appreciated well as well as my own personal residence, Im ready to step up my Investment game, how do I determine Optimum amount of  Equity to "Leave-in" if im ready to Refinance for Cashflow/Maint. ? Emotionally with the current world situation and potential inflation ,I "want" to pull as much as possible 70-80% so can re-invest in more properties  , but also want to be conservative with Rents being able to cover Mortgage and Maintenece costs. Im New to these calculators,just signed up to BP 2 days ago. any insight would be appreciated,thank you