

- Probably wouldn’t hurt to set them up, especially if you don’t have a static prefix. The good thing is that interfaces can have multiple IPv6 addresses, so they can use both the public address and the ULA.
- SLAAC should always be enough. Make sure you don’t block the ICMP6 messages it needs though (I’ve been bitten by that once, firewalld behaves weirdly around this).

You should be able to see pretty much anything from any instance. That’s kind of the point :)
It’s worth noting that old.lemmy.world doesn’t use my fork of mlmym (yet? I should write to them about this), so you are missing out on a few features, most notably user preferences, which you’ll need to go to the normal lemmy.world UI for. But that shouldn’t generally be a problem.
I don’t remember right now whether lemmy.world uses cloudflare (it looks like it does, for mlmym at least). There are probably other instances that don’t use it, but most will use some kind of anti-bot system. In the end, it’s a matter of choosing the option you’re most comfortable with :)
mlmym itself shouldn’t need any JavaScript, although some things will be slightly nicer with it enabled (voting, replying, and so on don’t require a page reload, for example).