two questions

I have been seeing those dragon eels about recently also, but I have never kept one. On the sump, yes you can have more than one tank connected to one. I couldn't work out all the details, but if you look at many LFS and LPS you will see they are all interconnected to one large sump.

Yes, you can run multiple tanks on a single filter/sump.

you can run a sump on multiple tanks but as what happens in some shops is if you do when one tank gets ill the whole lot may, and thats a lot of water to treat. I would also think unless your keeping many fish with same water params you would be stressing some of your fish? Am I wrong in that.

I have 11 tanks in one system. It has never had a disease outbreak (it has been up ~15 years), but I am very careful with QT - just exactly as I am with stand-alone tanks. QT has nothing to do with the filtration technique used, everything to do with protecting your existing fish from introduced disease and clearing any existing problems that come in with new fish before they go into their permanent homes.

Rainbows breed, Cichlids breed, catfish breed, plants grow and multiply - why would I want to do water water mods? The system is tap water. But obviously you cannot do water mods on a central system unless it is done to the whole system.

Central systems are notorious for spreading disease without prior QT of all residents. Consider both micron-level filtration and UV of the retuns to the tanks to reduce the possibility of explosive disease outbreak in a commercial situation.

the shutoff valve would be nice for other things but in my thoughts almost useless for disease control remember that water has been filtering for some time has contaminated the whole system already by the time you see the first sick fish. Imagine, humans being sick you were exposed to the sick person 1,2, 3 days or weeks ago so you don't necessarily know who got you sick.

I tknk the shut off is nice for locking the tank out of system due to mainantce things like leaks or other things.

Before when I was talking water modifications, I was thinking adjusting the params to what the various fish want. I know most of us in FW use tap water.

I certainly am a tap water user. I only do water mods if I absolutely must. The occasions when I absolutely must become more and rare with the passage of time.