Welcome to the forum!
Are the vets you're visiting familiar with chinchillas? The broken leg problem surprised me, with it still being at a 45 degree angle after 2 weeks. As you may know, lots of vets don't have much (or any) experience with chinchillas. As long as you're working with an experienced vet, you're doing all you can to fix the problem. Unfortunately, there are lots of chinchillas who have lost a leg/arm to a poorly judged leap, but I think most of them seem to get around ok with only 3 limbs.
With the swollen leg, I would pick him up and check for a scratch. If you can find one, you could try to treat it with an antibiotic cream. But if you can't find it, and maybe even if you can, it might be best to take him to the vet. Especially since it didn't swell up until a week after the cat "visited". That makes me think there could be a different cause. He could have injured this leg as well-and a tripod chin will get around much better than a bipod!
As far as the cataracts, I didn't know that chins could get cataracts. And I didn't really know they had pupils, being as they're so beady-eyed. So I'm going to defer to one of the lovely breeders on this site who have experience with dozens or hundreds of chins.
When it comes to the tail, there's not much we can do about that. I would treat it like a cut, and put antibiotic cream on it until it healed completely. I don't know if there's any special risks involved with the fact that a cat bit him off-certain infections you should watch out for, etc. Make sure Spatula doesn't get any dust baths while he has an open wound-you can hold him on your lap and rub the dust into his coat for him, that would make him very happy. But letting him roll himself won't help his tail. I would keep a very close eye on it and visit the vet at the first sign of trouble.
--Also, you should make sure to keep the windows closed when you're letting your little guy out. I've read that chinchillas can jump as high as 6 feet. Mine can only get about 3 feet, but that's high enough to get to my windows. With cats getting in and him possibly being able to jump out, you could lose him forever.
This is mostly my experience from researching chinchillas, some others might have input from personal experience. I hope we can help!
I'm sorry you're going through all these troubles and vet visits! Hopefully soon your chin will be healthy and you can both be happy again.