So it’s been a while since I have done a mod for Morrowind and an even longer time since I played around with adding a merchant to the game. I have discovered that I have need of doing so since nobody else has for what I need. Does anyone here know what all is involved with setting up added merchants’s store inventories?

I don't know, I never tried it.

I played around with it years and years ago. I was going to expand Seyda Neen by adding a Skaal style house on the little peninsula just west of the town proper. It would serve as a tavern that would house a bartender/general trader who would sell basic Solstheimian(?) weapons, armor, clothing, ingredients, and food items (specifically Nord Mead!). The plan was to fully decorate the tavern with bar furniture and add a few generic barbarian-ish NPCs (Nord, Orc, a savage little Breton), and a pier outside with a longship docked beside it. I don’t really want to do that much work right now, but I would like to add a merchant somewhere with a small stall that sells the above mentioned goods. I’m seriously thinking Seyda or Ebonheart would be the best locations for it.

Google it. Seriously, go into a search engine and type exactly what you're looking for. "Making an NPC in Morrowind" is a good start. Somebody somewhere has either made a tutorial about it, or a YouTube video. I am 99% sure of this, since it's a rather popular thing, I would imagine. If you don't find what you're looking for right away, keep searching other combinations of words. Next would be "making a merchant in Morrowind" or even better, "Making a merchant in Morrowind Construction Set".

Just wait 'til you start getting some rather bizarre modding ideas though. Like trying to stage a fight between two or more NPCs. Or needing to write a script to make a policewoman arrest the player. That's where I'm at. And there are NO tutorials for that sort of stuff; it's all trial-and-error. But for popular requests such as making NPCs or changing weapon/armor stats, I'm sure you'll find what you're looking for.

Well I actually figured out that merchant NPCs will sell stuff out of any container that is assigned to them as the owner. For simplicity’s sake, I simply added a bunch of crates in Arrille’s store room and now he is selling Solstheimian goods. Boom. Done.

Sometimes the easiest way is the best way. I thought that was how it was done but I didn't know for sure and didn't want to say something that wasn't accurate.

Are the crates respawning? Can you go in and steal everything from the the vendor's crates? And if you do does that mean the vendor will have nothing to sell for a few days?

When I was looking at how the mead vendor in Thirsk Meadhall behaves, the crate from which her mead supply comes from has the “References Persist” button activated whereas on most normal loot containers it’s not activated. I have yet to test it, but my theory is that because this button is activated, the vendor will always have 20 units of Nord Mead on hand. You could buy all 20, but then exiting and reentering the barter interface should replenish the stock. As for if crates that do not have the “References Persist” button activated replenish after a set amount of time, I honestly have no idea. How long in game time does it take for a crate to respawn if it’s going to?

That is true, some merchants always have the same products ready to go, while others must restock if we buy their food / ingredients. This restock seems to take 24 in-game hours, though I've never gotten scientific about this. Maybe we have to simply exit and reenter the inn for her to restock? Not sure.

An example of the latter is that lady who runs the inn in Pelagiad. I think if she has, let's say, bread for sale, we can buy this bread, which will then be gone from her inventory. It takes awhile for her to get new bread, but she always does.

But there are also some merchants who never run out of stock. There's a merchant who one of mine buys an endless supply of ingredients from, and she makes dozens of Fortify Intelligence potions from these ingredients. We can buy 10 at a time (10 comberries, for instance). Exit his menu, go back in. Voila, 10 more ingredients can be bought.

I have done zero modding in MW so far, so I have no idea how this works. Khajiit is ahead of Renee.

I like modding Morrowind! I feel that there’s a simplicity in it but you also get the sense that you could do almost anything with enough experience.

That's exactly how I feel about Oblivion, in comparison to Skyrim, especially with quests and scripting. My gosh. If I need to do something simple like add an item via script I can write that practically in my sleep, if we're talking the OB Construction Set! In Skyrim's Creation Kit I always have to slow way down and think about how to do this.

I’ve never even tried tried to write scripts. That just seems beyond me.