IF I want to maximize my system I would buy a pump that will push the 1325 GPM (figuring in my head height) that my stand pipe will swallow and use a ball valve to reduce it if required. Sound right?
Personally, I wouldn't want to screw with trying to adjust a ball valve while watching for the tank to overflow itself. Also, what are you rating your standpipe at? Different styles of standpipes will handle different flow rates and potentially offer different levels of noise. For example, a full syphon standpipe will drain more a durso standpipe design, but may also make more noise. I would figure out what your standpipe design will be, what it drain rate it can support, and pick the largest pump that after considering head height won't exceed the expected drain rate. Water on the floor is never fun.
AND use the largest sump that will fit.
Yes. Easier to maintain media. Easier to make room for equipment, and as mightiest_keeper suggested, you need to keep in mind having enough empty volume in the running sump such that during a power outage, when the water syphons back into the sump, it doesn't overflow.
Who makes a quality QUIET pump currently?
Mag Drive pumps have been around forever and get the job done. During my research, Laguna pond pumps seemed to also get great reviews and often used less electricity to move the same GPH as many other pumps. The pumps come in a basket prefilter since they are designed for pond use, but it can be removed if needed to reduce the space it takes up. I kept mine on since I had room in the sump. You'd probably be looking at the 960 or 1350 based on what has been shared. Here's a link:
http://www.lagunaponds.com/en_us/pumps/waterfall-filter/
