The stock 42T chain ring will give you about 27 gear inches and just 5 mph @ 60 rpm cadence in the lowest gear. That's pretty low. I would do a test run with that first. If you want lower, It looks like they have a 38T that should work well for you. Chain will likely need shortening. You might need a tool to remove the links. Don"t know about removing a crank arm.

I see you have steep hills, So yes, Go low. I see 38T options, Or 36 as suggested above.