First off I would recommend you update to Picard 2.2.3. Picard 1.4 is a very old release and things have improved significantly since then. Many advice you will find here does not apply to Picard 1.4, especially in regards to genres. Also the current lastfmng is not compatible with Picard 1.4, you need Picard 2 for this.
For Ubuntu 18.04 or later we offer the latest Picard version in our PPA, please see Downloads - MusicBrainz Picard for directions.
For genre I would actually recommend you use the builtin genre support in Picard 2.2, which you can configure in Options > Metadata > Genres. For folder organization you probably want to limit this to a single genre, so set the maximum number of genres to 1.
For the decades and original date it gets a bit more complicated. Picard has a tag %originalyear% which can hold the original release date, but this currently deals only with the first release date of a specific album. Earliest release date for a single recording currently cannot be easily supported. So even if you don’t care about the album you still will need to make sure to tag against the proper album or single (and not some compilation) to get the actual %originalyear%.
Second thing is writing this out as decades. You can quite easily use the %originalyear%, but there is currently no function to get this as the decade. Best way would probably to have a plugin doing this. Some people might also have this solved with some tagger script logic, but it would be a bit cumbersome.
Regarding earliest release date see also the following discussions.
You might be interested in using the “No release” plugin. It removes some tags that are only relevant when tagging releases (sich as catalogue number or releasestatus) and it can be configured to do this automatically. It also can be customized to remove additional tags you don’t care about.