Xyth & company have a couple of NPC mod(let)s that can do what you want. But, the complex AI (following, hiring) requires custom code, so you'll need to either use DMT, or use the Mod Launcher (which compiles DMT modlets automagically).
You may need to adjust or extend what's there, but that work would be up to you.
There are overhauls that add NPCs (like The Wasteland or Darkness Falls) but AFAIK their human NPCs are fairly basic, they don't used the options that need custom code (like being able to hire them or instruct them to guard your base). You can (and should) still check them out.
Adding biomes is another story, especially since RWG is such a moving target. Other people have tried to create new biomes, and from what they said, it's a monumental amount of work. I don't know anyone who has done it.
