would it make sense to host something on my main machine?
Not something that would have to be on all the time, but more something that can be off overnight.
This question feels like it has an obvious yes/no answer that I'm missing.
From experience I would say avoid this. I started my homelab this way. First it was a plex server just so 1 family member could locally stream movies without me having to copy it to a flash drive. Then another family member saw it, so it was 2, then 3. Less than a year later I have ~10-15 regular regular streamers and I can't play video games on my computer from the hours of 4PM to 1AM because my CPU was being hit so hard.
Eventually I built a new gaming rig, pulled out my GPU. Turned the old machine into a full time server and gamed on the new machine.