evil it dosnt cost that much if you shop around and find good deals you can get it cheep
mine is UNDER 600 a few things i did wrong and will need to change but thats all part of starting out
yup
you would olny need a small bag you dont have plants in marine tanks so you dont need lots for roots to grow in i would use as little as half a cm and 3 cm max unless you get some kind of digging shrimp or goby