Also Aquaworld nth shore, online as well wonderworld rotorua.
Sump as big as will fit in the cabinet allowing room for any other gear you may want to put in there.
I did this to heat my 3000 litre. It was fairly basic but ran the tank over winter. Without a thermostat control I would have cooked the fish, used 2 200 L insulated drums for overnight heating.
Sneaky2 has a system on the forum in reptiles and amphibs I think.
Yes you can but because of the way it is created it can contain heavy metals which require special tests to determine their prescence. IME I havent seen a marine tank containing scoria that has been running longer 12 months.