@Patrick2387 If we had a time machine, I'd recommend going back and shortening your maximum stay. Airbnb only collects the first month of rent upfront on long-term bookings, and all they can do if they don't receive payment after that is cancel the booking. But after 30 days, under California law your "guest" will have the right of tenancy, and it would take a long and costly ordeal to evict them, even if they stopped paying.
Hopefully, your first guests have a legitimate purpose for booking 3 months of accommodation in your area and this won't be a problem. But I'd be suspicious that they chose an unreviewed property for a commitment like that. As far as supplies go, it's ok to just leave a few days' worth of consumable stuff like TP and detergent. You just say during check-in that you've provided a starter pack of the essentials, and advise them of where the nearest stores are when they're ready to restock them. You're not required to leave supplies for the whole long stay, but it helps to be clear in the listing about what supplies you do and don't guarantee for the whole stay.