Questions on setting up a Large tank

I have designed a 2'x2'x8' wood and glass tank with a trickle filter. I am
going to be using sand as the substrait. The tank is 250+g. I am going to
use a 1/2" piece of glass for the front window. I have read about W/D
filter media and am still not clear as to how much I will need for a tank
that large. Also, how is the easiest way to heat the tank from the sump? I
was thinking of using a Hagen 901 powerhead for the return from the sump.
It is rated at 900 gph. Is this too large? So I need to have two sumps and
filters? I would like to keep a few Oscars in the tank so I know that I
will need a lot of filtration. Is there anything that I am totaly missing?
I have heard about hard-plumbing the tank for water changes and that seems
like a really good idea.