You can use multiple landscape actors in the same scene, absolutely no problem. You probably want to set higher resolution for your houses and lower resolution for the other 3 landscapes. I always use 2 landscape actors, one for the more detailed area and one for the outer area with less detail and resolution.
I’m a bit confused with what you say are your base materials? - I hope you don’t mean ONE big texture for the whole landscape actor? That’s not how it works. You would have a tiling grass material, a tiling dirt material, etc. Then you paint the path onto the grass material to create a blended path. I usually try to keep the amount of materials used to 4 per landscape but you could use more. I find the documentation on this site here for landscape a bit confusing especially the material part of it. Maybe there are some example levels you could download from epic.
If you have big textures for the 4 areas you would be better off using a static mesh (or 4 if you want to) instead of landscape.
Also maybe look into world aligned materials that let you blend different meshes or landscapes that intersect with each other without any clearly visible seems. This isn’t the best example:
