Some obscure bacterial infection. This was spread by hand and siphon. The point being the separate filters saved me 2 tanks exposure in the end most of my fry tanks ended up with symptoms and I had even been sterilizing everything in between tanks after symptoms showed. In the end if disease is a coming and its more than your average parasite then separate filters has never once saved me. The reason it never works for me is because I service my tanks at-least once a week. Typically if an disease is present it doesn't show immediately. In that even I'm spreading it around before the first tank ever shows symptoms of anything. Another consideration is simply cost. I can't reasonably afford to purchase or for that matter maintain multiple UV filters on 10-20 filters. I know that if I get something horrible it will f'ing suck, I just did that dance. All I could argue is that having easier consolidated maintenance with a better quarantine process will allow me to service my tanks more regularly keeping water cleaner fish healthier and disease on its heals. I have a 50 plus hour a week job and can't be committing so much time every week to fish. When I argued it was a illness I didn't mean I live for my fish I take really good care of them and try to provide the best I can manage but really there is a line between What I do for my fish and for me. Consolidating maintenance will save me, keep me healthier and more in a frame of mind to enjoy my animals. I simply haven't found keeping separate filters to make disease isolation much more effective when it comes to a truely malicious illness. Sure it stops ich but so does 86 degrees Fahrenheit, not really a challenge to fight ich if its the primary infection, same goes for pretty much any common parasite. I commend the fact you can care for your animals I simply can't. This is a hobby... a really consuming gratifying one but a hobby non the less, it can't be my life.
You do not need a UV for your tanks. Some people do need them for things they keep. It's recommended if you keep frogs, or turtles with your fish, but typical tanks rarely need them. I have UV's running, but only on my koi tanks because they are more prone to disease than almost any fish out there believe it or not.
I have rays, frontosa, flowerhorn, shrimp, puffer, SA/CA cichlids, bichirs, guppies, sturgeons... I have no uv's on any of them. I understand how you think tying them together would be best, and how if something has it, and you don't know, you can spread it even if individual.. but the chances aren't too high.
For me, (and this may work for you) my tanks go through a series of things, and so far it's been great and I've not had any issues with fish in over a year (with the exception of my FH with internals).. once a month, they get treated with something. This is how I work things.
Month 1: Temp 75 F, treat with .3% solar salt (skip water change for 3 days)
Month 2: Temp 72 F, treat with oxytetracycline (bi furan, binox) Leave in for 48 hours.
Month 3: Temp 76 F, treat with Ich tab Leave for 48 hours
Month 4: No treatment.
Month 5 resume.
Now, I don't always do this.. but when I was going through my KHA training, I learned that many people don't QT their fish correctly, and so many illness's don't come out until AFTER they have been in your tank for some time. Now, QT for Koi is 6 weeks long, and much more complicated.. but I have found that my rendition of it for tropicals has been pretty awesome. I had ich once in my 180 SA/CA tank.. my oldest fish, an 8 year old convict was on deaths door.. within 48 hours, he was ich free and back to his old self. I haven't had any issues since.
You stated: "I commend the fact you can care for your animals
I simply can't." If you can't care for your animals, then really... you shouldn't have them. Part of having fish is keeping good husbandry skills, and if you can't provide that, then you are only giving your fish a miserable life. Find another hobby. I often work 60 hours weeks at my job, and when I come home, I don't want to have anything to do with my fish, but I know that I took on the responsibility of keeping these guys, and so, I get up and I give them the attention that I promised to give them. Fish keeping is a rewarding hobby, and one day I do plan on making this into a career.
I am also going to suggest that you look into your fish diseases.. raising the temps, and salting won't get rid of everything, and for the things it does treat, it's eventually going to grow resistant, so you need to mix up your treatments. You stated that you had an incurable bacterial disease that killed off your stock.. there is no incurable bacterial diseases. Even if your fish had dropsy, it's still curable to a point. It could have come down to the fact that you thought salt would work, or you just didn't catch it in time.
Point blank: you can tie your system together, and do whatever you want with your fish; but when they come down with something, and you lose it all again... re think what I told you because you will be kicking yourself later for not doing things the better way. Separate is always better because cross contamination is less likely.