The interest pay day is at least 30 days after the last pay day. You can't find the last payout on steemd currently. If you have the cli_wallet running, you can get it with get_account cryptobro. The parameter is called sbd_last_interest_payment ... add 30 days and that is your payout date.

You don't need to manually move funds, to get your interest, but the SBD balance needs to change somehow. You could also receive a payout in SBD .. that's as good as moving your funds. A conversion probably works aswell .. can't tell for sure

I can't give investment advice, but if you think about compound interest, it seems reasonable to trigger a payout every 30 days.