Two of your three unknowns are answerable from Wix’s own docs, and one of the answers makes the availability limitation more serious than it looks.
Blocked time does not touch existing bookings. Wix’s Blocking Off Time article is explicit: blocking off hours does not override class or course sessions happening in that same slot, it does not affect existing appointments, and it only prevents clients from booking new appointments in that time frame.
So the failure mode is concrete. A member creates a twelve week series. The owner later blocks a week off for holiday. Wix keeps the occurrences sitting inside the blocked period, silently, because that is its documented behaviour. Your app does not monitor for it and Wix does not flag it. The owner finds out when someone turns up.
That is not a criticism of the design. It is the one thing I would put on the listing in plain language, because owners assume blocking time protects them and it does not. That assumption predates your app, and you will get blamed for it anyway.
Short of a background monitor, the cheap mitigation is a re-validation when the series detail view is opened, or a health check the member or owner can trigger. Not continuous, but it converts a silent failure into a visible one at the moment someone actually looks.
On packages you can go further than you have. Wix documents that clients can pay for group bookings using purchased packages on both desktop and the member apps, and that each participant consumes one session. What is not documented is the same mechanic for individual appointment checkout. Since you hand off to the native Cart and Checkout, the likely answer is that Wix applies the entitlement itself and your app never needs to know about it. That is worth ten minutes to settle rather than hedge: create a service, give a test member a package, create a series through your app, and watch whether checkout charges or decrements. A stated behaviour is worth more on a listing than a caveat.
Pricing Plans I could not verify either way from the docs, so your caution there is correct.
The mobile gap is the one I would close first. Recurring lessons and coaching get booked from phones more than desktops, and an unverified answer there is the objection that stalls the sale.