I'll go ahead and start with the sump, whole heartedly recommend skipping that and ordering a standard/custom glass/custom acrylic since it's going to be a lot more complicated for such a large system.
One issue you will run into running 2 pumps and having likely a 1.5" drain would be running a single roller mat since they cant handle more than a 1" full siphon (~2000gph) anything more will likely exponentially+prematurely burn through your paper usage through prematurely triggering the sensor. The 3 solutions would be ditching the roller (not ideal since you bought it and want less maintenance than socks most likely), purchasing another ($$$), or letting some water bypass the roller (i guess that defeats the purpose).
Since you already are going with a dual return system, I would simply recommend plumbing one as a manifold pump (if desired for uv/reactors/recirc skimmer/etc) that finishes into the display and then the other just being a simple return pump. Frankly if a manifold is not desired, I have since rescinded my old statement of recommending dual return pumps since it's entirely wasteful otherwise.
Definitely take the time to plan out what equipment you'll end up using for sure before buying/ordering anything as a sump and talk to a few lfs (if able) to see what they could order you as far as custom glasswork is concerned for a sump if glass isn't out of the question. Something like a standard 125g without a center brace (won't be as necessary due to baffles) would definitely cost a lot less than the bashea one you linked but have the advantage of having a 72x18" foot print (with a possibly minor disadvantage of being about 24" tall) I would hate for you to end up like some other fellow I saw here recently who couldn't sell his sump and had to cut it up just to fit something he bought
