New daily driver

As for the trans. Can I just unhook the overdrive and put it on a toggle switch if I indeed keep it? I already have a 904 ready to go on the shelf

Yup. But why would you? The switch that's in the dash is already a toggle, per se. It just turns the overdrive on and off.

And remember, the A500 is based off the 998/999. Steeper first gear and the extra clutch.