Hi bbzoe, welcome...

Yes, you can use one pump and run to two GB's. Use ball valves on each bed, so you can control the flow into them.

I've tried sharring a drain for multi beds with siphons, going back to the FT....it's easier with individual drain lines....IMO.
For 1st place info on siphons....Do a search for 'Affnan bell siphons'....he has lots of great info on how to set them up (and why they work)

Water pumps that I've been around, are all pretty quiet. A 600 gph sounds about right....'Danners' are a pretty good brand, with a 3 year warranty. They are only a few dollars more, then ones of the same size, you'd buy at the home improvement stores.

Air pumps are another story...some are quiet.. some aren't.

Aquatic eco-systems web site has lots of stuff to look at....and to drool over, like the piston air pumps they have on sale right now.....