Have I returned at the wrong time?

[Niwashi]

If things pick up I will purchase the new expansion but I thought I won't need it until i finish levelling and main story.

The only things the expansions unlock before you reach level 50 are the new races they introduced. So if you want to either switch to or start a new character as an Au Ra, Viera, or Hrothgar, getting the expansion now would let you do so.

After reaching 50 but before finishing the story, the only other things unlocked are the new jobs introduced in Storm Blood: Samurai and Red Mage. Besides unlocks, having the expansions would let you continue earning XP and levels rather than being level locked at 50 (though whether that's an advantage or not while still doing level 50 and below content is a matter of opinion).

For all other content from the expansions (new quests, dungeons, areas to explore, etc.) as well as the Heavensward jobs and some other new features (like flying) you'll need to finish the main story first, both the original story of ARR, and the story continuation that was added in the patches between ARR and HW.

Also yeah. If Party Finder was that sparse, likely also you're on during the off hours.

For a low level character, it's common for most PF listings to either show up as "Locked Duty" or not show up at all, depending on how it's configured. There's a setting for whether you want locked duties to show up or not. I don't remember which way is the default, but if his is set to not show them, then the only listings he'd see are ones that don't list what duty they're for except in the comments, and ones for low level duties that he's already unlocked. Since, as already mentioned, few players use Party Finder for low level content, there's rarely any of the latter, so PF can look a lot more sparse than it really is.