What do you mean by "timestamp" in #1? All the timestamps are in the database so it's just a matter of displaying them. Are you asking for the timestamp that an artist was last imported?
As for #2, artists are referenced via their "service ID" when importing. It checks to see if an artist on service X has an id Y and if it does then it uses the existing artist otherwise it creates a new one in the database. We don't have to worry about artists changing their names.
For #3 yes manual uploads are planned. Just haven't started working on them yet.