Don’t fret about the starter issue too much. Annoying that the guy won’t help you out, but you have it now, so you will likely have to deal with the issues yourself.
Can you do basic testing of the starter circuit, or know someone that can? If you can prove the starter is faulty, then try The Starter Motor and Alternator Company, usually good stock and prices, very helpful on the phone, and next day delivery.
Regy has already given you the lowdown on the track, inspect it for a missing lug in the belt somewhere, you will have to live with it or replace it, the track belt is not something that can be repaired once it’s shot. Plenty of suppliers for those though, ask on here for a few names if you decide to change it.
Can you put a pic up of the button on the joystick? Are there one or two buttons? When you press the button/buttons is there any indicator lights illuminated on the dash? To indicate the change from a fixed boom position to a swinging boom?
It may be the microswitches in the stick. Likely not be a dealer part as a separate item, but entirely possible to change these switches if they are faulty.
A pic of the machine and the sticks will help with further advice
