Hello there

1) Leveling other jobs for the story, Doing hunts to upgrade equipment, Doing Beast Tribe dailies for even more story, Hunting the Fox Lady FATE, Triple Triad
2) Good question. I'm loving the Stormblood dungeons so far (beside Doma Castle) and all the trials. And the Outfoxed FATE. And I still enjoy Palace of the Dead. Oh and Lost Canals of Uznair.
3) Funnily enough new systems mostly come up in patches and actual expansion releases only add more story and dungeons. Rival wings was a pretty new addition. We will get more new stuff this month with 4.2
4) I play once a day. But that one time is several hours long. You don't really have to unlife it asit is very easy to get enough item level for new releases.
5) That's easy. 3 and a half months. There are sometimes staggered content between huge patches, but big ones with raids and dungeons and a whole lot of other stuff come every 3 and a half months.

Bonus: Well the absolute hardest content is Ultimate, but that is only one fight so far, so savage raiding is the top. As for housing. It is controversial. It had a lot of content related to it but it is not instanced so a lot of people can't get into it.