Mr. Grumpy Gills;3500426; said:its a good idea. it simplifies fish keeping.
The more water you have the better, so by running one sump for a lot of tanks basically you have one very large tank. The advantages are temps and water chemistry wont fluctuate as fast. Also ease of maintenance, you would have one point for filter cleaning. Also you can set up a trickle system to your sump to completely eliminate water changes. Bad things are disease can spread easily and catastrophic failures like if you have a heater go out it will affect all your tanks. If your using one pump and that fails.........If your not doing your scheduled maintenance (filter changes ect.) you impact every tank in the system. Quarantine tanks are a must, even and most importantly for feeders.
The two pump question: Lets say you add another tank to your "system". All you have to do is drop another pump into the sump and run that line to the new tank. The new tank will have it's over flow plumbed back to the sump so all the water you pump into the new tank runs back to the sump, done. You wouldn't have to cycle that new tank either.
If your have one large pump you would have to build a manifold with a bunch of valves on it and then just tap off a valve to your tank. Use the valve to throttle the flow to your needs. Of course you need to pay attention to the over flow capacity so you don't put to much water into that tank and it can't drain fast enough! Been there done that.
If you have a "fish room" the one sump system is the way to go, good luck!