We've been self-hosting GitLab for about a year now, and I don't remember it ever going down or being unavailable. We self-host almost everything else too (except for online meetings), and it's all been pretty stable as well. Some of the tools we self-host do go down occasionally, but it's usually just a matter of restarting the VM or adding more storage.
Recently on Hacker News: https://news.ycombinator.com/item?id=48833116 (Chatto went open source) so you might be able to self-host your online meetings pretty easily too if you wanted to. (They're not the only option in that space, either, although they are one of the easiest to spin up an instance of that I've seen thus far.)
Do you serve the instance on the public internet or on a VPN?
I've been thinking about self-hosting myself, but for my purposes (open source), I'm worries about scrapers and other sources of DOS-like traffic.
VPN, accessible only from inside the corporate network
Do you self host chat?
Yes, Rocket.Chat