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Sorry but absolutely impossible to answer your question as it will vary on every cruise.
If there are lots of unsold cabins then lower offers will be accepted. During holiday times ships tend to run full so no or few MoveUps accepted.
I note that recently suites on most cruises have been reported as sold out - try a mock booking on a TA site - thus only vacancies would be a last minute cancelation. A mock booking can give you a guess at if suites are sold out
Yes, you would have access to the Retreat.
Also know those in the Captain's Club get bonus $ for their status.