I am looking for a way to keep all of my workspaces hot. Is there a way to do it with SSH workspaces or is it possible by hosting the IDE on my own server?
it is not possible yet.
You control the compute behind your SSH instances, so you can choose to turn them on and off as you please.
In summary, yes you can have unlimited hot SSH workspaces because the concept of hot workspaces in Cloud9 does not apply to SSH workspaces, seeing as you control the compute .