Cash reserves, emergency fund, operating acct, security depo acct

[Kikko Maeyama]

Hi. I would like your advice and experience. Does a new one-apartment rental business need all 4 accounts/funds?  Can I put a security deposit in the operating account until it is returned to a tenant instead of opening a separate security deposit account? And are the cash reserves and an emergency fund the same thing? Thank you for your help.