I believe there is a plugin (I've not looked into it) that will stream to multiple destinations (content delivery networks [CDNs.. ex YouTube, FaceBook, Twitch, etc]) at once. As Aaron mentioned, that requires bandwidth and extra hardware resources on the part of your OBS Studio computer (especially when not all CDNs accept the same input settings. Encoding multiple outputs may not be insignificant load depending on settings (low bandwidth 1080p30 is one thing, real-time encoding of multiple 4Kp60 stream is quite another). Using a service to handle the re-encoding and distribution may well be worth it if you don't have the onsite expertise, redundant WAN links for uptime assurance, etc
You absolutely can run your own server... by someone with sufficient technical (operating system, hardware, and software) skill. beware.. this is NOT for the 'feint of heart'.. this would be a significant undertaking for a viewership of any material volume ... and gets complicated quickly (entirely doable, for someone who knows what they are doing, has the budget and network connections required, etc.... ).
this is NOT in the realm of easy end-user do-it-yourself (well, you could get it up and running, but don't expect it to stay up without real subject matter expertise). And then you have to ask yourself what uptime expectations are there? will this be a 24hr x 7days a week operation. And what happens when a computer needs a reboot? is downtime (not streaming) ok? just food for thought
OBS Studio is a compositing tool (combine multiple sources), so if one of those sources is what you consider a commercial... sure, it can handle that. Personally, I'd being looking at something like Advanced Scene Switcher (a 3rd party plugin) to automate the changing of 'Sources' to 'play the commercial (video source) at a scheduled time