If you are just using the cart around the neighborhood and not loading it to excess or trying to turn it into a hunting buggy you can probably go to 48v without all the rest of the electronics.
That conversion would give you about 30% more speed and torque but will be a little rough on the components. The motor will be fine with 48v. Make sure all your connections are clean and tight. If you have too many issues, you can always do the controller and pot box later.
If it runs under heavy load, inclines or hunting you will need to do the full conversion. Cost estimate for that is in the $1200-$1500 range.
BTW, nice updated silver and black look!
