Mamiya RB bulk film backs

I want to get going on using my RB bulk film backs. If you know anything that can get me started ie: 70 mm BW film purchase source, clever handling hints, etc. I welcome your reply.

I used to shoot a lot of 70mm vps. I recall two concerns: you need to learn to be able to test a short strip, so you won't have to expose the whole roll and learn of light leakage or whatever. Secondly, you're handling a lot of money at the loading and unloading stage. I mistakenly exposed a whole roll once to the tune of about $100 in an instant...

JY