Q1:
I believe they would need:
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Save Artifact > Create an artifact for an import.
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If they are also modifying an artifact, importing a CSV to update existing artifacts, then Modify an artifact will also be required.
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A CSV import may also want to create folders so the Save Folder option should also be available, I do not know what would happen without that set, it may work and just put the imported artifacts in some existing folder.
I would set those.
Q2: "...always using a Change Set." - Yes and No, Yes you can set it up for change sets, but have to be enabled and required.
Note: if you do NOT use change sets for everything, then everything is a change set and if you use multiple streams, when you deliver from one stream to another, each change to an artifact shows up as a change set. (e.g. change an "a" to an "an" in an artifact - a change set is created.) Before we understood change sets, we had not enabled them and had generated 40K+ change sets that will live forever in out DB now. There are many advantages of using change sets and not many disadvantages.. just my 2 cents worth.