de_Monteynard: When playing Morrowind, I would also recommend the 'Less Generic NPCs' mod in addition to the Overhaul mod. Why? Because as the title says, it makes the non-plot relevant NPCs far more engaging and gives them a backstory of their own. They couldn't populate the entirety of the world, mind you, but it is sufficient to break from the monotony of the original (and also Skyrim from my experience). Plus you can also add some Great Houses material as well, but it's all packaged in a way that allow you to cherry pick what exactly you want (more precisely which location you would like to mod).
HGiles: I actually really didn't like the LGNPC mod, the added dialogue broke immersion pretty badly for me. It was so obviously an add-in, and even if it was decently written didn't fit with the world or the culture/race of the NPCs talking. So I don't think it's a good recommendation.
I only ever heard people saying that about the very first LGNPC mod, which has nothing to do with today's LGNPC except the name. Did you perhaps play that old one?
Explanation: One modder released a mod that was called LGNPC and that gave every NPC in Seyda Neen unique dialog. It was a great idea, but the implementation was quite crude. I still remember how Eldafire (a high elven woman) was given some completely inappropriate dialogue about priests abusing her as a child. Apart from not fitting into the game world at all, this is definitely nothing that one would tell a complete stranger in the first conversation ... and if an author touches on such a sensitive topic, he really needs to elaborate more and not use it in such a careless manner.
In any case, the mod was crude, but the idea got traction. Many modders got together and wrote individual dialog for all NPCs in certain areas, which was based on the world's lore and written under the premise to read similar to things that Bethesda might have written if they had had more time during development. And they really succeeded with that. The author of the original LGNPC mod was never involved in that project, and his mod got redacted after a while and now fits much much better.
HGiles: Morrowind Comes Alive was much better, especially with the children patch to add different ages in.
Morrowind Comes Alive introduces lots of NPCs with no dialog at all. The companions are pretty good though. But the main problem of this mod is that from version 5 onwards, it adds enemies even to areas which are usually safe (like the center of Seyda Neen), and these are pretty strong. For someone who just starts out with Morrowind and isn't already used to the chance-based combat, this creates an awkward experience: You enter the world, walk a few steps, and get inevitably killed by a seemingly overpowered enemy, in the middle of a town, while the guards twiddle their thumbs, and your own attacks never hit although it looks like they would. Are you sure that you want to recommend this to first-time players? ;) Which version of MCA did you play?
tinyE: Does it matter which mod I install first? The GCD or the MGSO?
Shouldn't matter.
Unless you're playing rather old mods, install order shouldn't matter at all, since every mod puts its files neatly into its own folder. That's a standard that the community developed after a while, when we found out that having 250 mods which all dump their files into the same folder isn't such a great idea. ;)
Load order is another matter and can be very important if you use several mods which work on the same thing. But MGSO and GCD touch completely different aspects of the game, so load order shouldn't matter either.