Firstly, when you remove the water, due to displacement, you wont need to neccesesarily need to add more salt because all your really doing is reducing the water volume and not just salt conent, so, in theory the salinity, if it was correct will stay the same..
Its always fun and games, learning the little pit falls, learning how it all starts off with hands on, rather than reading on a web site or a book..Its never the same as how you imagine it to be..
Sounds like you doing ok mate..It will all be fine..let the water ciculate for a good while and get your salinity and temp up to correct levels, get your rock in there and any more sand as needed...then..................................................................................................................................wait........................................................................and wait..............................................................................................................and wait.....................and..........................................................................................wait...
Patience is now your best buddy in the world, with out it, things start to go wrong...
enjoy it all and keep reporting back to us, and of course, supply us with some pictures through the stages...
Niko