credit/debit memo request

hi,

1) credit memo request - After create invoice in vf01, then if credit memo needed, must create credit memo request in va01 then only can create credit memo in fb75?

2) debit memo request - After create invoice in vf01, then if debit memo

needed, must create debit memo request in va01 then only can create debit memo in fb70?

3) credit/debit memo can only be created after credit/debit memo request is created?

4) if credit/debit memo not created in fb75/fb70, where in sd can create?

5) credit/debit memo request done via which tcode if not va01.

thanks