I used around 60 lbs in my 55 and it looks nice, goes up a little higher then the plastic base.
Again its all depends on your taste. Some only run 1-2" others run 6+, I like to have 3-4" so I would get 1 lb per gal
and have about 5 extra on hand. This would be good for a 3+ SB. i think there is a SB calulator on the home page??
Good switch you will be happy with the sand bed.
I got LS
for my reef and i used southdown play sand for my fowlr
and is there a major difference NO
.... So look for a safe paly sand and use that and then get a few lbs of LS
and seed the top layer. Good luck..