Overall the list looks really solid for what you've purchased so far.
I see that ultimately the ac route vs a chiller wasn't suitable for you (which is okay) but it would've been nice if that worked out

Since you're local to tenecor, it might be worth taking some time to get a potential sump quote from them as well to simplify buying from a bunch of different places (unless the price difference is far too great out of their favor)
Alternatively if you were going the route of Advanced Acrylics/Tsunami (FIshtanksdirect) for the sump you can do the same with them for a display + possibly a stand.
A few suggestions to add based on the other items mentioned:
You don't really need ultra fancy heaters (looking at those titanium heaters). A few eheim jager + ranco nema4/whatever the aquarium rebrand is called heater controller is essentially unbeatable as far as reliability (technically any heater + ranco falls under that) It's an industrial thermal controller thats meant to handle frequent on and offs and depending on the model it can handle running a chiller if the temps go too high as well and you wont run into the issues of a premature outlet failure that you might experience on an apex outlet (if that was what was controlling your heater)
Do not over do the usage of unions. They're commonly an added unnecessary expense and even worse yet, an additional point of failure. Put them in areas which you know will need servicing (such as a UV depending on plumbing) vs every loop and corner where there really isn't a point in ever taking that apart unless you know you'll move in a really short span of time.
I also strongly suggest talking to an electrician to add a few dedicated breakers and additional outlets for just an aquarium of this size. A 450+ gallon potential tank (not even counting sump volume) consumes a **** ton of electricity and having one single shared 20 amp (or worse yet 15 amp) simply will not cut it. Assuming I'm remembering correctly a 20 amp breaker has a max load of 2400w
As far as water storage is concerned/mixing is concerned, as long as you can get in there comfortably and keep it clean/serviceable then that's ultimately what matters. You don't want to overdo it and end up with a rats nest of a mess in there (or literal one for that matter)