I'd probably feed 3 or 4 rat pinks IF he'll accept multiple items. (some snakes won't- most likely due to being more shy than hungry) Pinkies are more water than nutrition, they digest very easily. Yes of course you can still switch after you feed off the pinks- not to worry. You're only changing the size, & snakes pay a lot more attention to the scent. (rats have a different scent than mice)