1) As a user can apply multiple tags to a track, it is more than possible to get more than 5 tracks with 30%.
2) Are you sure it's missing out tracks which are then completed later? I would expect some tracks to be missed out because results cannot be found, but not otherwise.
3) Nice idea, but a little complicated for this script as it would need multiple calls to Last.Fm - but another script could be written to do this.
@Chake - I'm learning the ins and outs of SQLite at the moment so this script certainly will be updated to have these two modes working in MM3, but I can't say when. Lots of scripts to do!