So... what now?

[Risvertasashi]

I currently have both MCH and WHM at 80, planning on maining MCH but keeping up to date with WHM for roulettes (faster queues, plus as much as I like DPS, I love healing). I bought a full Exarchic set for my dps and have been buying 490 pieces with my tomestones for the WHM. Is that sufficient to go into endwalker? or must I invest the gils in a 2nd Exarchic set, least my healer class be rendered useless?

Should I focus on unlocking all the optional dungeons, trials n stuff? I unlocked the Ruby weapon trial but it looked extra complicated in the guide I watched so I haven't dared queue up for it. Should I? Is there a point? What about the alliance raid? (don't even know what it is to be honest)... Are relic weapons still a thing? Should I try to do my MCH one or is that stuff for the more hardcore raiders?

I tried looking up guides n stuff but they all tell me I absolutely need to do about a million things I clearly won't have time to complete before it's too late.

HALP!

I would not worry about optional side content - at least not as a necessity. The main things I suggest, based on your interests and as general necessities, are this:

• Inventory. Clean out your armory, and general inventory, and really all forms of inventory. You don't want to go into an expac and then have to stop at some point because you ran out of space and need to clean up.
• In line with the above, make sure your gear for each job you will be playing is sorted out and ready go. You'll replace it, of course, but good gear still gives you a good start into the expansion.
• If you plan on leveling the new jobs, prepare level 70 (Augmented Scaeven) gear set for each.
• Might seem obvious but - do finish the MSQ, don't get sidetracked with other stuff on that.
• As others have mentioned, the current alliance raids will help you upgrade your gear. 490 is enough if you buy gear from NPCs are Endwalker's release but I'd personally shoot for 520 if you can. 530 would be "excellently prepared."
• If you have an abundance of time or just need a side project, you can pursue a relic weapon. They're good and some of them look cool. HOWEVER, you will replace your weapon in the expac quickly enough that 5 extra ilvls won't help much. If you get an upgraded Cryptlurker weapon, that is more than enough.

Annnnd... that's it, believe it or not.

You don't need to do that much. Gear, inventory, and MSQ are the bare essentials. to be well prepared. Everything else, you can do because you want to or for more minor reasons.

Good luck!

Edit: Oh, one more thing.
As a healer, when a new expac releases, you'll be dealing with a surfeit of tanks in crappy gear. So, even moreso, if you can compensate by having the best gear you can get, it can help a lot.