$4lb if it's cured is a good deal. The stuff at my LFS
is 5.50 a pound cured which is considerably more, but pretty much every piece has a tiny colony or two on it. Even if it's not cured $4 is still nice especially since you can pick out each piece yourself.
You can just cycle with pure ammonia and add some bacteria (probably sell it at your lfs
) until the cycle is done. I don't know about salt mix or RO
as I have a 24 and the deal they have at my LFS
where buying $10 worth of stock gives 10 gallons of salt water free gets me all the water I need. If you plan on corals Elos makes wonderful test kits, and seachem makes good "cheap" tests for nitrates, ammonia, etc.
Don't put bioballs or anything like that in the bins. Add GFO
if so inclined, but really sponges and carbon are all you need.