I don't think it's worth paying for gear on the marketboard at this late stage, except possibly a weapon. You're better to get what gear you can while completing content. You only need to reach i490 to clear all story content and i495 for the highest "casual" content (the third alliance raid), so paying for i510 isn't necessary just to get through it (though it does of course bring your average up).

On the other hand, do check whether the crafted gear is something you'll want long term for glamour. If so, you may as well buy it now while it has practical use on top of the glamour value.

If you wait two weeks to do the 5.X MSQ you'll get free i490 gear from it.

If you'd rather get into it sooner, you can start building up your ilevel by completing the 5.X side content starting with the Eden raids and possibly the first part of the Bozjan Resistance quests to get your free i485 starter relic weapon.

You'll also get a good amount of the mid-range "allegory" tomes from roulettes if you do them with your level 80 character, along with a smaller amount of the top-tier "revelation" tones, so you can be decently geared quite quickly even if it's a bit of a patchwork of different tiers.

Outside of the endgame gear treadmill, the story writer for Endwalker has recommended that you do the Binding Coil and Omega quest lines if you haven't already. (She actually recommended prettymuch all the side stories in the game, but singles out those two as most important.)