[Delphinus]

I'm kind of wondering if 64x turnover might be a tad on the wild side for the livestock you're thinking of. It'd probably be awesome for an SPS tank but if you're thinking of things like open brains, Euphyllia (torch/frogspawn/hammer/etc), Plerogyra (bubble), you could probably make do with a bit less. On the other hand, maybe they'll still do OK but the flipside would be that you could probably save a couple bucks if you went with some smaller pumps.

You may also want to go with BB. If it were me I might try a 1" sand bed but be ready to go BB instead if it kept shifting around. 64x turnover is a lot, I have probably more like 20-30x turnover on my cube tank and if I don't have things pointed "just right" then the sand ends up in a big pile in the corner.

I ran my old ritteri tank (72gal bowfront) running the sump return and skimmer off the same pump. It worked, but I found that that I had to valve back the sump return line in order to drive the pressure up enough in the pipe to drive the skimmer properly. This was because it was a non-recirculating style skimmer. With a recirculating skimmer, you don't need the feed line to be pressurized, just provide a little bit of flow. I can't remember the exact recommendation for optimal skimmer feed flowrate, but I think it's somewhere near 1.5 times the system volume per hour. Anyhow, basically, not very much, so the majority of the flow from the pump would still be available for the sump return or closed loop or whatever you're using it for.