Hi welcome to the forum!
Unfortunately a 55g is too small for tangs. :-(
In order to get anemones you will need some awesome lighting, what do you have in mind?
I have a eshopps refugium and it's good quality and sturdy, i like it very much. Not sure about their wet drys though.....I also have an in sump skimmer from eshopps, their psk 150 and I'm pretty pleased with that as well. You will need an overflow box to get the water from the tank to sump btw if you didn't already plan on that.
Also as far as live rock and sand, I would aim for between 1.5 lbs per gallon and 2.0 lbs per gallon. Since your'e doing a FOWLR
you can get away with less rock than a reef tank.
As far as sand, I would say about 75 lbs should be good.