Giving notice to a strata manager depends on the conditions contained in the contract with them. I believe that the usual time is 3 months notice.
As far as finding a good strata manager, best to ask around. But a good strata manager can only be really good if the owners/owners corp keep on top of things. You really do have to make sure that they are attending to issues that you have asked of them. I would always ask in writing and ask them to respond in writing that they had received and understood then would follow up if I didn’t see/hear anything happening.
I did not consider our SM very good, however I did realise that they had more than our complex on their books and that most complex’s would have had some issue for them to attend to most weeks if not most days. So it is necessary for owners to follow up with their own issues to ensure they are not accidently overlooked.