Seems to me like you’re thinking clearly about this. Unless someone else with hands on experience jumps in with a pro-tip I suspect you may just have to pick your poison and give it a go.

Multi-lemmy isn’t a common config, though. Lemmy.world and I think lemmy.ca do it, but even lemmy.ml which was the biggest instance 2mo ago doesn’t. There might be half a dozen people in the world with hands on experience at this.