How do I get an int of the number of players in every server?

I've seen people can use leaderboards that update every 5 minutes or so to check the top 100 player's leaderstats, however, is there a similar way I can get an int that updates every 5 minutes that shows he number of players in every server?

You can use publish async to send the number of current players in the server And subscribe async to receive the information List every message you get on the leaderboard and there you have it

https://developer.roblox.com/en-us/api-reference/class/MessagingService

At the moment, no, there is not. I know that you can do something like that with the Games API, but you'd need to use HttpService to do something like that.