For your current set-up, the Pamela's New Workout should be plenty for setting up multiple clocks. You don't have to divide a clock if your clock source can output multiple clocks in sync. For your small set-up a divider wouldn't be all that necessary.
Get the Poti for the Batumi. It's the one thing that should have been STOCK on the Batumi. It's well worth the $60US.
As far as a mixer, Blue Lantern's Stereo Sir-Mix-A-Lot. For the price and the feature set it's hard to go wrong with it. It's about $225US. For your next expansion, consider a quantizer, sample and hold, traditional ADSRs, and possibly one of your big effects modules (ErbeVerb, Z-DSP, Magneto, etc.).
What you have should be a lot of fun to begin with. I assume the DrumBrute Impact will be handling the sequencing portion of the build?