Had another run through with some of the Eastercon people this evening and it's now making a little more sense. Still feels a bit of a childish environment, and I'm still wondering how well it will work with several hundred participants trying to access the same site, rather than the 6 that took part tonight. And it would be nice if they had even one bald bearded icon... Anyway, most of my problems went away when I used headphones and Firefox instead of Safari as the browser. It appears that Gather.town doesn't have the fairly robust noise cancellation of Zoom etc. and makes older browsers fall over due to its animated displays etc.
I was also told that the software that will be used for conference participants (and to watch panels etc.) has roughly the same hardware etc. requirements as Zoom, so with luck it should be OK. Feeling a little better about the Eastercon anyway.
Later - forgot to say that I was contacted about program participation a couple of days ago, so that's more or less sorted too.
Also posted at https://ffutures.dreamwidth.org/2226535.html, where there are comments. Please comment here or there using OpenID.