Well, this is my third time heading back into Morrowind. The past two times I've played this game, the only mods I used was the Morrowind Graphics Overhaul (a wonderful mod, by the way) and the Morrowind Code Patch. That was it. This time, I'd like to go back into Morrowind with a lot of mods.

What type of mods am I looking for? Well, for one, your personal favorites. Yes, yours. They have to be your favorite for some reason. To be more specific, however, I'd like mods that increases immersion in the game. I don't want mods that turn Morrowind into Star Wars or something.

I've heard a LOT about Tamriel Rebuilt, and I'd like to know, is it worth it?

I'd also like a mod that improves the leveling system. It's not that I hate the vanilla leveling up system, but I feel like it can be "improved" or "overhauled".

If possible, I'd like an improved combat mod. I know there's the "Accurate Attack" mod, but it doesn't work with the Morrowind Graphics Overhaul for some reason. Plus, the mod makes putting points in your offensive skills worthless.

Lastly, I'd like to know how I'd manage all these mods. Should I use BOSS? Will it work with Morrowind? And what utility should I use to micromanage these mods (like the Oblivion Mod Manger or Wrye Bash for Oblivion).

Thanks.

For a hugely modded Morrowind, the tools you will want to be most familiar with are:

Wry Mash: This can do SSSOOO many things....HIGHLY recommended. Download the Stand Alone version https://github.com/Yacoby/Wrye-Mash/downloads, Read about it http://wryemusings.com/#WryeMash.
MLOX: Sort your mods into the best load order (the sequence the mods load into the game in). Based on countless user submissions to Dragon32 who currently maintains the rules base. Download http://code.google.com/p/mlox/downloads/list. Make sure you grab the latest mlox-data file from that link as well. Read about it http://code.google.com/p/mlox/wiki/Mlox.
Tes3cmd: Mod cleaning, Leveled list merging, and Mod comparison are my biggest uses personally. This thing ROCKS! Download from MLOX Link, get version .37v. Read about it http://code.google.com/p/mlox/wiki/Tes3cmd. Read my thread in my sig for easy to use mod cleaning too
TESPCD: Helping Resolve Conflicts. Download http://mw.modhistory.com/download--7040. Read about it http://www.uesp.net/wiki/Tes3Mod:TES_Plugin_Conflict_Detector.
TESTool: Only for Merged Objects Plugin. Download http://mw.modhistory.com/download--5234. Read About it http://www.uesp.net/wiki/Tes3Mod:TESTool.
Morrowind Enchanted Editor: (referred to as MEE or more commonly EE) Invaluable tool for editing when you want to dig DEEP into a mod. Download http://mw.modhistory.com/download--1662. Read a little bit about it http://www.uesp.net/wiki/Tes3Mod:Enchanted_Editor.
TESAME: For when you want to do simpler things than you would use EE for such as delete GMSTS manually. Personally I seldom use it, as I prefer EE, but some people like it. Download http://mw.modhistory.com/download--5289. Short tutorial http://www.tamriel-rebuilt.org/?p=modding_data/tutorials§ion=38054.
NifSkope: More of a modder's tool, but sometimes you might want it so you can fix something yourself like I had to do http://mw.modhistory.com/download--6375 (see additional file). Read and Download http://niftools.sourceforge.net/wiki/NifSkope.
A grep tool such as TextCrawler: Used to figure out what mod a problem may be from. For example, You have a message in your Warnings.txt file that says "Missing object "furn_de_p_stool_01_MCA" for reference during cell "Molag Mar, St. Veloth's Hostel" load." We will assume you do not know what MCA is You use the program to seach all the esp and esm files in your Morrowind\Data Files\ directory for any mods that have the text string "furn_de_p_stool_01_MCA" If you get TextCrawler, make sure to set the File Filter block to *.es?

I would definitely recommend Tamriel Rebuilt, it practically doubles the game map in a very lore friendly way. Tries to add mainland morrowind into the game, and so far has done a pretty good job of it. Textures aren't as high res as a lot of the stuff you'll see from the overhaul, more along vanilla morrowind levels. It's not done, so you'll need to update when new versions come out, but what is done is very good.
Would also draw your attention to Province Cyrodiil, and Skyrim home of the nords projects, that have similar aims in other provinces, but so far all they have released is alphas, so more one to keep your eye on, and maybe install if you want to take a look around (although there isn't really a legitimate way to get there yet, so you'll have to use console commands, or water walking/levitate for a looooooooooong time).

I'm surprised at the amount of tools there are. I probably don't need to use some of them, but I'll definitely download Wrye Mash, MLOX, TESPCD, and Tes3cmd.

Oh, so that's what the mod does! I thought it just changes the vanilla landscape, similar to how Unique Landscapes was for Oblivion. Based on what you've said, I'm wondering if I should get it. The mod sounds great and all, but it'd be weird to use it with Morrowind Graphic Overhaul, yeah? Wouldn't it be out of the ordinary to walk through textures the Overhaul improved and then into the less-HD textures of Tamriel Rebuilt?

Hehehe...Those are the ones I use most for making things play together nice or making something function correctly. I actually had 3-4 more I thought about listing, but decided to leave them out as they are not normally needed by users.

As to TR....yes it add a lot of land, many mods will not play nice with it. You might want to take a peek at my thread on GHF for http://www.fliggerty.com/phpBB3/viewtopic.php?f=28&t=5764 as well, to help you decide what landmass mods will play well together.

It's been a little while, but honestly I don't remember it being jarring enough to warrant not having it. A lot of the mods included in the overhaul do effect it to a greater or lesser extent, like better bodies, and distant land (although you do have to rerun distant land generator after it's installed), and so the issue is mostly just whatever unique textures TR came up with. While I really wish someone would develop some hd textures for TR as maybe a separate download, I would say that for me, the quality of the work involved and the way that it really fleshes out the world (not just a solitary island floating in the sea now) makes it more than worth it.
Also, the next release is I believe attempting to integrate mournhold into the great city area of almalexia into the mainland (the setting of tribunal). I'm suitably excited.
Finally, there's a few videos on youtube you can check if you want as well, mostly of people doing panoramic shots, but they might give you an idea of texture quality.

Many things in TR use vanilla textures, so they will appear updated like the rest of the game.