A note of caution, changing bags turn into saunas in just a few short minutes. Film doesn't like to load onto plastic spirals when there is moisture present. Learn to start the film onto the spiral before loading into the bag, this means while it is still in the cassette. Never rewind the leader back all the way into the cassette. Just trim ith end square, start in the reel, close the reel and film in the bag and finish loading. It is super easy to snip the film flush with the cassette when you get to the end.
Sorry, I should have mentioned this. I'm doing only 120 film so no cassettes.