Interactive exhibition space

Hello,
I'm looking into multiplayer solutions for the first time.
What I'm trying to achieve is a multiplayer exhibition space built to WebGL where visitors can select avatars and walk around in an exhibition and communicate with the other visitors via chat or voice chat.
It would also be nice for visitors to be able to hang up sticky notes in parts of the space or even be able to upload images and place them on walls.
I want the whole thing to be accessible for at least two weeks nonstop with all the visitor created content remaining in place.
I'm not sure which networking service I should look into for this matter.
I have already looked into Photon but at this point I'm not sure whether this is the right solution for just setting up a server where people can connect without a host running the 'game'.
Can anyone point me in the right direction?
It would also be great if the suggested solutions had a free plan for me to test whether I can make this whole thing work without investing money first.

Thanks in advance!
Ben