I'm considering one for myself as well, and all I can say is definitely try to handle an adult of each sex (for the size difference) and see how comfortable you are with them, if there is one size you're more comfortable with, etc.

As was said above, though burms are generally known to be docile and very tractable, every animal is different and there are also some very defensive burms as well. I'd suggest maybe getting one as a baby and getting used to the temperament as it grows with you, or look for an established adult that has been handled often by the owner because it'll more than likely be hand-tame.

I also want to bring up the food thing, would you be able to get feeder rabbits reliably? And do you have anyone nearby who would be willing to come and help you should anything go wrong?