Mr. and Mrs. Dayak, I will help you with building a sump the best I can although it is always wise to seek other set up to see what you like best.
IMHO It is very important for tank placement where Monster water volume can drain easily. I have my dirty water drain down to my basement sump, which then pumps out side. Every system has to be engineered accordingly. With My sump design, the micron filter socks keep my water
extra crispy(Working on a new video for my arowana community grow out and you will see my crispy water soon)!
sump is a mirror of my sketch.
Like in every sump there is Mechanical/Bio/Return and mine is just this simple. There are many, many, MANY... different set ups for a sump like drip plates, blah, blah, blah... I decided to go very simple with the basics and it works for me.
With a little DIY, I would like to share with you how I do large water changes next. I plumbed pvc pipes down to a drain and with a 180 degree turn my water drains 50%. So I can walk away and have a beer. When you are ready I will personally make a video showing you how my system drains.
So you guys have had experience with caring for smaller fish in the past which is great. The only difference I see in raising monster fish is the fact that you will spend

thousands of dollars instead of

hundreds on set up and filtration. But after that initial plunge, maintaining does not really cost that much compared to other hobbies

. Unless you become a fish hoarder(wife is starting to call me this

).
I think its Outstanding to see a couple both enthusiastic about fish keeping. You guys can pick my brain all you want although I am an arowana keeper in training myself still and always learning from those with successful systems.