primary google calendar for shopmanager

I already set up Appointments+ but I am baffled with Google Calendar API set up and very new to this, can someone please explain or give best approaches.

I want to set up to have each website (Multisite setup) with Apppointments+ will have it own google calendar synchronizes with the plugin so the website has its own calendar for staff to access.
1. What is the correct way to set this up in Google API? ie. should I set up new project for each client WITH their sub domain url.
2. How do I assign shop owner google calendar ID instead of ours.

Thanks