NO. You need not enter any opening balances for individual residential units. The balances for all the flats will automatically reflect in the new accounting period. Similarly, the balances of vendors will automaticlaly reflect in the new accounting period
However, you need to update the opening balance of all accounts under Chart of Accounts (Bank and Cash Accounts, Accounts Receivables / Maintenance Charges Receivables, Accounts Payables, etc.) with appropriate opening balances.