I have used 75 gal tanks as sumps for decades.
I don't see the need for baffles at all.
I use filter socks for mechanical filtration, put bio-media in mesh bags, and substrate in containers to jump start other tanks.
The pump, heaters, and other stuff just lay around in the bottom, of the sump.
I have also used 50 gallon barrels as sumps, they ca be whatever you want them to be, the simpler and easier to pull maintenance on, and adjust to evolution as an aquarist the better.
I first went the baffle route because that's what was the trend, but I found baffles limited space, and for experimenting with new ideas, and got in the way when doing maintanece.
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Above is a 75 gal tank as a sump where I added a bio tower,fractionation unit..
below same sump, with heater, containers of substrate and other paraphernalia.
below biomedia in mesh bags (very easy to remove and clean)
filter socks hanging in the sump for mechanical filtration.