I feel like you'll want a switching frequency in the 10+ Hz, at a minimum, for a motor, (better if it was much higher), and <1 Hz for sure for a heating element controller, (unless you really wanna kill your SSR quick). "Range" in the controller doesn't matter. The frequency does not change as you turn the potentiometer...only the % the circuit is "on" for each cycle. (So with a 1 Hz PWM, 50% means it's on for 0.5 seconds, off for 0.5 seconds. 25% means on for 0.25 seconds, off for 0.75 seconds).
A switch to switch caps would be easy peasy....a DPDT switch, low voltage, low current, would do the trick.
Really though, they cost ~$10 max to build...why not make two dedicated ones, so you're not having to switch outputs between the SSR for the element and the motor?