How does Marketplace work on TLP?

For things such as exp potions, mounts, bags, etc?

Well no mounts til Luclin. If memory serves, xp potions took a few days, I could be mistaken on that though. The bags they sell initially are crap. Spend the real cash and buy from this link. You can buy the packs that are on there right now, and then buy the ones that go live tomorrow. These will no longer be available after today. Race change potions will be available.

Oh yeah, most if not all illusion items will be available. Same for familiars and pet illusions. Hero's Forge will be as well. All the other potions will be too, really the only two useful ones in my opinion, are the mana and speed potions.

You can get all the normal buff potions - clarity, run speed, haste, regen, lev, etc. Exp potions also.
I would add daybreak cash before launch but I've always been able to reclaim for exp and buff potions almost immediate at launch.

Side question, what about Origin and Lesson Of The Devoted?

Origin yes, lesson no (not until DoN)

Origin immediately available, the rest of the vet AA's start showing up at Dragons of Norrath. https://forums.daybreakgames.com/eq/index.php?threads/nerfing-vet-rewards-after-this-long.262415/

Origin is available day one once you hit lvl 5. You can find it in your AA window and make a hotkey.

Vet AA rewards become available in DoN according to Fanra's wiki: https://everquest.fanra.info/wiki/Veteran_Rewards

25% exp pots are available day 1. 50% pots become available later when Luclin unlocks maybe? Not sure about 75% pots but I think they're available on Aradune right now (PoP).

As soon as I'm ready to hit the newbie yard I buy the SoW potion. They are 4 hours, persist through death, and give you (I think) max speed. Even when available, the player-made SoW potions are useless for level 1s because they use caster level to determine speed.

I have to run from Halas to Commonlands fairly soon, so I'll be picking a speed potion up. Already got my bags from the old pack, so I can pick up the new pack when my wife isn't checking the credit card bill.