DIY filter questions

im going to start building a 75ish gallon tank for my oscar this coming week. ive got the measurements, and my plan was to section off the back(like.. add another wall) to seperate the overflow and the tank. something like this:

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|..........................:tropicalfish:........................|
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the green bolded part is where it will overflow, the comma is where it will come out, and that lil colorful fish represents my oscar. i was looking at Sploke's 220 or 200 gallon build for his turtle, and thats where i got this idea.
Any suggestion on how to set it up? im still a little confused about the filter part. Should the whole back be filled? and the water should go through eggcrate sections with mechanical in one section and biological in the next, then out of a bulkhead?

forgot to say that would be the view from above

i did lol. just not sure of how much water is supposed to be in there, and how to match the overflow rate with the GPH pump/bulkhead exit rate. or does the overflow intake rate depend on the pump exit rate? hm, that actually sounds right to me.