Opening balances

I am coming from another a/c package and will start using sage as at the  beginning of May, July is the start of the financial year. I have setup my nominals and entered my suppliers and am about to follow the opening balances guide as at 30/Apr

Regarding supplier balances, is it okay to enter each as a lump sum as at the opening balance date per the guidance rather than enter each o/s invoice?

There are some supplier accounts that payments have been posted to but no invoice received,  for these would I select the credit option?

Lastly, the next VAT period runs from  Mar - May how does will this work in terms of the invoices which were posted on the old system in March & April?