Not a finished solution, but here's how I would handle it: Without using some sort of browser script (with tampermonkey or similar), Roll20 data is pretty walled off. I think the easiest way would be to build a display in a mod script-updated user handout. Said handout would display current stats for whatever you want to track. Since the handout would contain script-generated content, you could style the heck out of it with HTML and CSS to make it as pretty as you like. Pop that out into its own window, and make that window an OBS source.
