Everything sounds great to me!
Just make sure to be checking all of the tubs, as heat rises and there can be some variation between them.
However, mild variation and changes are to be expected!
Otherwise, the humidity is good (it can be upped to 70% for shedding). I don't think you'll have anything to worry about with too much humidity, simply because it doesn't sound like that'll happen. If there's an odd day here or there where it drops to below 50/40%, or bumps to above 70% (say, if it's raining outside and the humidity in the air is high in general) I think that would be totally fine, so long as it is not constant.
If you get the snakes all from the same place I don't see a real reason to quarentine, as they've already been in contact with each other - unless otherwise stated/advised by the breeder.
This may be difficult, but try not to walk into the whole snake-handling thing with a scared/nervous attitude. Be positive! It seems pretty infrequent that BPs bite, unless occasionally out of fear when they are hatchlings. Any animal with teeth can bite; I'd be much more nervous about a dog or cat bite than a snake bite! If you are nervous though, for peace of mind as you say, keep a glove handy. I personally don't think there is a need for a snake hook right away, especially if the snakes are little. Mind you, a bare hand will get them more used to you because they will be able to smell you and feel your warmth more-so than through a glove.
Best of luck to you and your sisters!