For a history of companion mods, try
here. For the best group of companions (in my opinion), try
here.
But I would first suggest picking up a copy of Ghostwheel's
TESTool. Read the documentation. You use it to clean mods of extraneous comment lines, and to combine lists, objects and dialogs in mods. It also compares mod content to the original game, removing mod data that conflicts with Morrowind.
You run companion mods same as you would any other. Unzip the files into a temp directory, then copy over each sub-directory to its appropriate Morrowind equivalent. Run TESTool, and clean the ESP and/or ESM files. The TESTool "Manage" option lets you indicate which mods you want to run. When you've finished, you simply run Morrowind. TESTool will already have added your mod choices to the main game.
Be sure to check the companion mod documentation regarding what each companion can and can't do, and where you can find 'em. For example, Laura Craft can't follow you on a Mark spell; in fact, she will tell you this. But she will offer to meet you back at her house, in a temple, in the Vivec plaza area (she enjoys shopping), etc. She will give you a ring that allows you to communicate at a distance. -So in all cases, read the documentation.
