Hasn’t been an issue for me. HA would only be depending on Opnsense for a DHCP lease so assuming you have reasonable lease times it’ll just pick up where it left off.
Without checking I would imagine you could just set a delay for the HA container to make sure opnsense can start first, if it does become an issue.
A long time ago I used something like sockd to run a local proxy and then send that data to my personal remote proxy server over port 80, something like https://win2socks.com/ I think
Maybe there’s something better than socks these days.
Back then it worked pretty well, but I don’t think they were doing DPI. They (admin guys) did seem to notice large file transfers and seemed to be killing them manually.
I would assume most places these days will collect net flow data at least, so while https will protect the contents, they will be able to see the potentially unusual amount of data moving back and forth to your proxies IP.
I would suggest at least using a VPS to hide your schools IP address from the irc servers. And you may be in serious trouble if you get caught. If you’re in the UK you’re going to be risking jail time, and speaking from personal experience, they take this shit seriously.
So maybe just set up a personal hotspot.