Let me just start with a warning. Your freshwater experience gains you almost nothing in the way of saltwater. No offense intended, I have about 5 years freshwater experience and had no clue of SW
requirements. I quickly realised that I knew nothing. SW
is alot of work and personally I would reconsider your plans, IMO
it wouldn't be worth the time and cost to just support a crab, but hey you may love the little guy.
I spent more money on sand and rock in my 29G than I did last time I had the driveway redone! 8O
Live rock is pretty much exactly as it's name implies. Well the rock isn't alive but there are all kinds of life on and in the rock. bacteria/coraline algae/worms.......The same applies to live sand. Any sand or rock will eventually become live considering it has the correct inviroment to do so. These organisms are all part of the biological filter.
Yes that salt will work fine, DO NOT USE TABLE SALT!!!
what type of crab is it?
you may or maynot catch some slack from fellow enthusiasts for wanting to use fish for cycling. It's common for some to be upset by one of two reasons
1) adding fish to an uncycled aquarium puts it's life at risk
2) Many of these fish are pretty agressive and won't play well with others. So you are buying a fish that you will probably just pitch aside later on.
GL with what you decide. Just remember that patience is a virtue in the SW
research research and research some more. Theres hundreds of DONT'S for SW
that were DO's for freshwater. Don't buy anything or add anything to the tank until you know the consequences.
For a reference, search the net for converting a freshwater to saltwater. You'll find alot of info that you'll prob miss out on by just searching for SW