It's now just under 24 hours since I announced the forum and the support page, and I have 2 subscribers, both at the Coffee + Sandwich level.
This extra £12 per month is enough to pay for increasing my podcast hosting plan from 160 MB/month upload limit to 540 MB/month. That's the equivalent of being capped at around 3 episodes per month, versus being able to upload up to 9 episodes per month.
Thank you so much guys, and I hope you enjoy the Zulip forum! :)