My main concern is that your competitive advantage seems to be that you are a free /open core chat tool, but this advantage also attracts many bad customers. They'll want a chat tool that features-wise rivals a competing (paying) platform, but also with the added twist that, by being somewhat open-source, they'll also want support for their weird edge case setup that you didn't consider ("Why won't this work on a Raspberry PI?", "Can I use this on my company's intranet?", "Do you work on Windows 3.1?", etc etc).
You'll add in more features and support for these things, only to find the rabbit hole going deeper and deeper -- and identifying the customers that are actually willing to pay becomes harder and harder as you have to filter out a lot of the low-quality requests.
To help with filtering, you can push people to the hosted version where they have to pay, but now you've lost the competitive advantage -- and have to compete with the many other chat tools in the space.
I think there's still a lot of room here, in the same way that Gitlab carved out a huge niche from Github, but those would be my main concerns.