"I would make the withdrawal that costs me the least in transaction fees
and allows my money to continue to grow at the greatest "safe" rate until it's needed for expenses."

Make your best guess. Change it later if you need to. Be aware that you MUST keep the calendar (tax) year amounts "substantially equal".
I've been doing this for three years now. Started with twice a year and switched to four times a year. Talk to your IRA custodian for costs on each transaction. Consider direct bank transfer rather than "a check in the mail" which keeps your funds out of any interest bearing account for at least a week. Be aware that even though your fund will do a direct transfer which is essentially instantaneous they may debit your account several days ahead of the actual transfer. (read Schwab)