Raid quest-line starting points?

[Iscah]

I have no Heavensward Raids for that reason, although I *think* the Towards the Firmament quest will get me there. I'm saving that for an alt job.

The Firmament is essentially an epilogue to Heavensward, with a number of "nice" story quests and a focus on crafter/gatherer content.

However, even if was raid content, it's not worthwhile putting it off to level another job. They don't give much EXP and the quests tend to just give gil as rewards. Though if you've only got one job altogether I recommend picking up a second one anyway.

Anyway. The key thing for finding raids on your own is to look around the major cities for "blue" sidequests that will unlock something.

Some of the raid and trial series are worth doing as you go along because they involve MSQ characters or provide details that help you understand later events.

ARR: In addition to the Crystal Tower and primal trials you had to do, the Binding Coil adds character development for Alisaie and was one of the recommended things to play pre-Endwalker.

Heavensward:

The Alexander raids (starting in Idyllshire) are stand-alone but provide some background for a thing that happens much later on.

The Warring Triad trial series (starting near Fortemps Manor) ties into a few things, none of them critically but I would still recommend them to be done sooner rather than later.

The Shadow of Mhach alliance raids (Ishgard airship landing) seem to be disconnected from anything besides a few level 50 optional dungeons, although there is a small possibility that one of the villains has future significance. For now there's no need to do it.

Stormblood:

Omega is recommended, but you're already on that one.

The Four Lords trial series will come up along the path of the MSQ. It is optional for now but they do seem to like having certain characters from it turn up randomly in seasonal quests (twice so far).

Ivalice alliance raids (starting in Kugane) are also very optional for now. The only somewhat useful thing for MSQ relevance is that it unlocks the level 80 Bozja storyline and the first part of that involves Cid's backstory, but that's not critical either.

Later expansions:

I won't go into detail as you're not there yet, but Eden (unlocked in the main city) is basically an MSQ offshoot, the trials series again comes up in the path of the MSQ and is currently non-critical, and the NieR alliance raids are not connected to anything.

Pandaemonium seems to be filling in the details of something we don't currently understand, and the alliance raids (yet unreleased) probably will be too. We have no idea what the trials will entail yet.