Questions about NPC and biomes

Hi, so I’m new to the game, just started a few days ago, and right now I have a giant tower with all of my NPCs in there, BUT I just learned that certain NPCs require certain biomes to work at their fullest. So my idea is to build a giant tree just like this image, but with different biomes inside this giant tree, and my question is:

Is this doable? Or does the game don’t work like that? For now, the only information I have about that is that to create a biome, 75 blocks are required.

And if this is useful, I already beat the Wall of Flesh and I’m currently in early Hardmode.

Thanks in advance for your responses.