Matrix

It depends on how active your homeserver's rooms are, how many federated rooms you have (and their activity levels), and how many images, videos, and files are being uploaded to your server. I would imagine that having a lot of bridges to other services would also increase the resources used.

I've looked up whether or not a Raspberry Pi could run a Matrix server, and from what I remember it seems like storage space would be the biggest issue if you have active federated rooms, or rooms with a lot of image/video posts.