Here's my plan based on the previous post and info I've received.
I'll use a gate valve to control flow through the system. 6 stages: sediment, catalytic carbon, sediment, cation DI, anion DI, mixed bed DI. All refillable containers except the sediment. I'm going with 2.5 x 10 due to my somewhat low water volume requirements.
The kit BRS sells comes with the TDS meter so that will have readings at: the inlet to DI, before the mixed bed DI, and output of the DI.