Q1.) I tried to run multiple sensors within a single experiment cell (shared buffer solution), but have observed what I think is cross-talk between the devices (particularly when running 2 electrodes for electrodeposition). Are there any issues I'll need to consider here?
Running multiple Rodeostats in a single cell (shared buffer) would be problematic. This issue is that the Rodeostat (and potentiostats in general) actively control the potential between the working and references electrodes using feedback. So when you have multiple Rodeostats in the same cell these feedback control systems can interfere with each other e.g. when the first Rodeostat adjusts the current sourced by its counter electrode in order to maintain the correct WE to RE potential this will effect the WE to RE potential of the second Rodeostat, and vice versa, etc. I think your best option here would be to isolate the test cells if you can.
Q2.) I sometimes experience more noise in my experiments. I was thinking about just swapping in larger caps on the TIA but it doesn't seem to happen all the time. Another thought was that the power being supplied by my USB hub might be contributing. Any reason to worry? What's the best way to power the rodeostat externally while using USB for serial comm?
You might try adding a USB isolator - not too expensive (~$35). Maybe something like this
Q3.) I see the P15, P16 (5/3.3V jumpers) next to the expansion headers as one option. However, I assume I would need to somehow physically disable the USB-provided +5V power away from the board?
It is possible to externally power the Rodeostat, but doing so requires requires cutting a small trace on the underside of the teensy 3.2. This documented on the PJRC website https://www.pjrc.com/teensy/teensy31.html See the images (further down the page) showing the underside of the teensy 3.0, 3.1 and 3.2. In the upper right corner of the board there is the trace which needs to be cut - there is an arrow which points to the trace and callout the describes cutting in e.g. "Cut to separate VIN from VUSB ... etc.".