This is where you need to use the closest available P4 profile wheel. Sources: AGW, Branchlines, and - if you have all the time in the world - Ultrascale.
You'll probably have seen the CLAG site which has just about everything under the sun for CSBs, seeing as they more or less invented the modern interpretation of the system.
It's probably safer to have split chassis AND split axles.
If you have a rigid axle, chances are that axle is the one that would make the model lurch. Only one axle driven per bogie - a total of two axles out of how many? It might be a bit underpowered.
If you're going to be making your own gearboxes and gears, why not try making bevel-and-spur gears? Lower rolling resistance, higher efficiency.