I am glad to hear Larry had a better afternoon I can't offer advice on all your questions, but I do have a few recommendations.
First, give him as much pain medicine as he needs. If he has had Tramadol before and tolerated it well, that would be a good addition. It will keep him comfortable, and hopefully "sedate" him a bit.
Second, if you don't already have an assistance harness, that would be a good thing to help him get up and around. Since he already has some hind end weakness, this will be a help even after he recovers from his current problems.
Third, if acupuncture is available in your area, I think it could really help him, both with his current pain and his back end weakness.
for you and Larry, and a little white light for the poor kitties who caused all this, not really their fault.