They can be quite a handful to the uninitiated.
Just so you know, he would definitely come off worse against the dogs.
Unfortunately several rescues have shut down over the last couple of years, and the ones that are left have had to pick up the slack, and have called upon all their friends to take in extra ferrets, so space is at a premium. Most of use are already 3 or 4 ferrets over what we should really have.
Ferrets are monsters for picking up when people are scared, and even the tamest will try it on if they think they have the upper hand, so I am not surprised you are feeling a bit nervous, even for long term owners it can be hard to work out what is playful over zealous nipping, and full on, going in for a hard bite, until it is too late with unfamiliar ferrets.
Not sure what you are feeding him on, but they can be quite fussy eaters, and if not eating properly will also be far more nippy. James WellBeloved do a Ferret food which is pretty standard, and most will eat it, and for short term use, the "Pets at Home" is OK, although it does make their poo stink, and is definitely down near the bottom of the ladder when it comes to good ingredients, but easy to get hold off. If you have any uncooked chicken wing tips, he may even go for them, and they are good for something to chew on, and distraction while you catch him etc.
Good luck with sorting him out a permanent home, and well done for trying with the little guy, they really do need nice people like you, who will take them in and try, as they die so quickly when left to fend for their selves in the wild.