I don't want lots of congealing growths... how would the "quick disconnects" work? Would you be able to quick disconnect from the intake into the pump?
You could hard plumb it with stainless or copper and, after running cleaner, run hot ass water through it, to sanitize, at the end and air dry. I assume you'll be doing that with the plate chiller anyway...
I would think it would make sense to run disconnects w/ short hosing from the kettle, vessel, and mash, and anything else you want to easily remove for cleaning purposes.
If costs are a concern, copper and brass valves will make it relatively inexpensive to plumb--even with all the valves.
It looks like a good idea to me, with the one pump and all. The first setup I built was a similar type of one pump design. My first a was a three tier. I put the sparge vessel on the bottom (pretty much ground level) with a copper coil hard plumbed to recirculate mash. The top was the mash vessel that gravity fed into the boil vessel, which was on the second tier (while the pump ran to sparge). After the boil, the second tier was high enough to gravity feed into a fermenter.
Your design eliminates a tier and incorporates a plate chiller driven by the pump. I am not a fan of plate chillers (don't like things I can't see are clean), but I think this design will work well.
The only downside I see is that you can't heat the mash as it fills the vessel (unless you put a burner there)--like you can if you were filling the boil vessel directly. That isn't anything but a time concern though.
Edit: the second design is simpler. Also, there are three main disconnects I have seen: Plastic high temp, sometimes you can find them that stop flow after disconnecting--this is nice but harder to clean. Camlocks, cheaper stainless disconnects--most popular probably. And morebeer offers another stainless variety that has a cleaner look and full 1/2" flow. I use the latter--they are more expensive, but I like them best.
you can look at photos in my gallery for pics of the quick disconnects.... i use them pretty extensively on the system pictured there....