Hi and welcome!
I'm not sure about the exact issue you are encountering and I know nothing about Macs.
Assuming you can use GP2Edit with wine or something like that, you should download the zipped package from
this page. This is the program you will use to install carsets (make sure to have it configured with the correct GP2.exe path).
About tracks, if you are having problems with convert.exe (in order for it to work it needs to be called from DOSBox), you can try using
my converter which doesn't require DOSBox. Make sure you have the correct jam folder names and also, start GP2 from GP2Lap so the track infos are loaded correctly (not mandatory, but very very desirable).
If you have more specific info about the issues you are getting, I can try to help.