You can find more Schedule 80 plumbing parts from Lowes. I don't think they carry aquarium quality bulkhead of the local hardware store. You'll have to buy it at the fish specialty store. For your overflow, you should build two Durso Pipe Mods.

That's a good deal on the RO/DI, I easily paid more then twice that more mine. I wonder how long their RO filter is rated for?