ok well im just starting as well but i think i can offer some info.
First off filtration is a lot different than a freshwater tank. this is the perfect article for you to check out: http://www.tropicalfishkeeping.com/m...shwater-31955/
no u cannot use pool filter sand, the best type would be arragonite live sand.
yes you would need live rock. about 1lb per gallon, but that differs between types of rock.
no not all fish and corals mix together, some corals have different light requirements. some fish will fight. stocking a saltwater fish tank is a lot different then a freshwater one. not all fish will suite your tank, it even comes down to the rockwork in the live rock with some fish.
Oh wow jellyfish tank. that would be huge, like the size of ur 2000gal tank. that is a big goal.
oh ya also the bigger the tank the better, i would reccomend starting with a 75gal tank if u have the money and space. The reason is because if something goes wrong in the tank you will be able to "see" it in the water, all the params will be wack. im starting with a 10gal and i can just tell its going to be a huge challenge to see changes coming.
THE BEST THING IN SALTWATER IS PATIENCE!
hopefully wake, pasfur (please come back we need u!) and some others will come and pitch in, im sure i left a lot out.
(i use enter to space my writings :P)