Congrats on the new snake!!
I would suggest that feeding prekilled mice is much better than feeding live, serveral reasons:
1) it's cheaper
2) dead mice doesn't smell as bad as live ones...
3) saver for the snake since it doesn't have to take the risk of getting hurt by the mouse (when feeding hoppers or adult mice)
more reasons if you want....
Probing is one of the ways to determine if the snake is a male or female. Poping is another. But both of these methods should only be done by experienced breeders or vets. Since both of these says COULD damage the snake.....and it might not be able to reproduce later on. So if you don't know how to use either one of the methods, please do not try it yourself unless you are shown how to do it by an experienced herper or vet.
Good Luck and Happy Herping!!