building a sump for a 450 gallon tank. Couple of questions

I am debating on what route I should take on building the sump.

I have the option of building it out of a 125 6ft tank or 2 75 4ft tanks. I want to lean towards the 2 75's asI have a few to choose from.

If I was to go with the 2 75's, I was thinking of connecting them via bulkheads that are already in the thanks upper corners.

If I go this route, would having the mechanical on the first tank (intake) and the biological in the second tank be a wise idea?

The tank I have setting up also is plumbed for a closed loop system, so If I had a return pump in the 2 tank and a return pump in the first tank hooked up to the closed loop would this be a good way to go?

Or should I do everything in one tank which would be the 125 6ft tanks.

Thanks

Rich

Thank's I tried the search an didnt find any thing for those user names