The Frsky radios run the OpenTX operating system, so you can go to the following link to download OpenTX companion to simulate and test the programming options of the radios.
https://www.open-tx.org/2019/01/06/opentx-2.2.3
I thought the 32 channels were only for advanced mixing, but I just learned that apparently these radios can actually transmit all 32 channels if you install an extra transmitter module and run two receivers. Might be worth looking into.
My plan is to use a switch to flip the sticks between driving and fire fighting mode. Sounds like you'll need to step up to an Arduino Mega too. Mine is currently doing fine running 6 servo channels, reading 11 switches and controlling lights on close to 50 pins. With an Arduino in the vehicle you can also potentially do stuff like clicking a switch multiple times to select different functions in the arduino, to combine simple on/off functions on a single transmitter channel.
I'm not saying the frsky radios are definitely the best option, it's just the only ones that could do what I needed within my budget. Futaba makes some great reliable but expensive radios. Scaleart has a VERY nice radio if you have an unlimited budget:
https://scaleart-shop.de/en/Remote-control/Commander/