The bites off a rat will swell up the first few times but after that they get pretty immune to their bacteria just give them a wash with saltwater and they should be fine. If it's a really bad one then use whichever treatment necessary.
Birmingham roller. The flight time depends on allsorts like feed, fitness, moult and weather but normally about half an hour, the rolling takes it out of them and tires them out imo.
I'm not saying it's right or wrong but the ferrets you're describing are the ones the old blokes around here used to recommend taking out hungry to fire them up a bit. Might be the kick up the arse they need?
Our wilko had a few sizes and loads of other stuff which twats had mixed up all over the place so I had to stand ages trying to get my hand in these little boxes picking m 8s out from all the other boxes and emptied the m 8 box too, I grabbed some smaller ones to try and I think they are m6? I wonder if they are selling more m 8 than anything else now?