Sounds like the combiantion of cured, populated live rock and LFS
water gave you an instant cycle. I did that with a new 155g tank, 100 or so lbs of live rock from my previously populated tank, a bit of old sand also, and 5 fish or so. It was more likely the cured, populated rock that gave you the instant cycle, not the water I believe. P.S. - if that "live sand" was in a bag, nothing was really alive in it. Just something for new life to take up residence in. Still a good thing though.
Sounds like you're on your way. Go slowly so that fish additions don't overburden your good bacteria population. Keep watching the nitrates and ammonia as fish additions are made to make sure you're staying balanced.
Is this gonna be fish only or reef? Let us know so we can help yu with what goes in next maybe. Sounds like you should do some snails now. Astreas, turbos (small ones), nassarius (for the sand beds), and a few other types might do now. Maybe 1/2 to a dozen for now I'm thinking. Noticed any algae yet? If not, you will soon. Also look up diatoms also. You may have a run of that too soon.
I would also recommend the pwc
now. Use aged and aireated SW
. Mix it today and maybe use it tomorrow evening. I'm thinking 15 - 20%.