New tank setup advice needed

I ran a 30 gal marine aquarium over ten years ago. I have come into
the possession of a 55 gal tank and want to start a new marine
aquarium.

Back in '91 the only filtration system I had was a Skilter 250.
Although it worked fine for me then, I assume there have been
changes/improvements in both knowledge and equipment in the last ten
years so before I buy another Skilter I thought I'd ask for advice.

My desire is to run a tank that will be almost exclusively
crustaceans. The only actual fish I plan to have in my tank is a
Mandarin.

My plan at this point is as follows:

Fill tank with sal****er
Let sit for 24 hours with pump running
Buy a bunch of live rock
Leave tank alone until rock is noticably active with food for Mandarin
Buy Mandarin
Slowly add crabs & shrimp

My questions:
Is a Skilter 400 a bad choice?
If so, what alternate is recommended?
Is my setup plan okay?
Will the live rock by itself be sufficient to cycle the tank if I give
it long enough to do so?
Should I go with a sand or gravel bottom?

TIA

sand will provide more food and better denitrification.