Any advice for a first playthrough build of Morrowind?

No mods. Play Vanilla first, you'll appreciate the game for what it is more and it will enhance your experience with mods later.

EDIT~~

As for a character, I personally prefer a Khajiit thief, but lately I've been having a LOT of fun playing a Woord Elf archer. [both custom classes]

Even if it's a vanilla run, the Code Patch and the Patch Project are necessary. There's no need to endure the bugs that would come with a complete no-mod run.

Personally, I would recommend Better Bodies/Clothes/Heads as well, but that's because I abhor the vanilla bodies.

They aren't necessary. But they are good to have, I still don't think that he should install them for his first run though.

EDIT~~

Talking about the patch projects.

As for Better Bodies, etc. I still don't think he should have anything but default Morrowind + Tri + BM installed.

I nearly always play a Breton mage (High intelligence, high willpower, high magic skills), but having high strength and high combat skills does yield a more playable character, especially in the early stages. Magicka doesn't replenish unless you sleep or drink a potion, so that in a battle you quickly find yourself out of gunpowder.

idk i had to deal with the game without patches till a few months ago when i got internet. now i kind of miss not falling through the floor or odd ball crashes and tribunal and blood moon having issues. been having three installs and moving save file between the folders for years.

but yes vanilla morrowind is a great way to start off. some textures just look way to different from what it started off looking like with any graphics overhaul stuff. i havent seen any that really stayed true to the first morrowind look. so first run should be vanilla

I assume you've already played another TES game? IV or V?

As for class, Answer his questions the first time through just to see what he suggests. Then go back and look through the different pre-set classes to get an idea of how they're structured. You might pick one of these for a first play-through (I like the Bard), but some of them are very unbalanced IMO, so I almost always make a custom class.

Major skills: I pick only one of the four levels of armor. Likewise, only one type of melee weapon, and often a type of ranged damage as well (marksman or destruction).

Minor skills: Speechcraft and Security are helpful support for anyone. Either acrobatics or alteration to get to out of the way places.

Of course, what you do depends on how you want to RP. The game is all about immersion. We all know the Morrowind combat system is not very good, but we don't play it for that. Combat is just a means; the reason we still play this is to participate in the world. And I think you find that world to be in many ways more subtle and complex than the other...well, that would be getting off topic....

actually i do play morrowind for its combat over the later games combat.

And you mentioned that this is a RP build. Any idea what kind of RP you're going to do?