Yeah, definitely use your temp gun. Focus especially on the head since BPs rely heavily on their heat sensors. Once you've fed enough times you'll be able to tell just from experience when the prey is warm enough.
As for not cooking it, just make sure you're not thawing and heating with anything too hot. I always let them fully defrost before heating too.
Ok, since it was just dirt/Coco coir you've got nothing to worry about.
And yes, definitely try to feed when they're in their hides. My only snake who will eat when not in a hide or burrowed is my Kingsnake. But he'd eat as part of the Super Bowl halftime show in front of a soldout stadium, hahahhaha.