I think the important thing is that people know these questions should be asked eventually, but I agree it can be later.
Too many people are giving the advise "it doesn't matter" but for all the reasons you mentioned I think it does matter a lot. You should consider your first account a throw-away while you start to understand Lemmy and what a home instance means to you, then be ready to ditch it and start fresh (until account porting is implemented).
I think it does matter, actually, as some instances get blocked and unfederated. But, there would still be so much access elsewhere it may not matter much. Generally, I would take a best guess at a first instance, see how it goes, and be open to making different account elsewhere as needed.
I have been lurking on the GitHub, and it seems quite a few people want the ability to port your account from one server to another. It was initially dismissed and the request was closed, but people made good points, like what happens if a server shuts down? Folks on that server just lose all their history? Those comments got lots of thumbs up reactions, and the request got reopened.
Hopefully at some point we can get that feature and making the wrong early choice will matter less.
Agreed, I want that too. But also, what if the server shut down before you had a chance to export and move it? Could accounts be mirrored on to multiple instances as fallback backups? would be nice. Could accounts be 'semi-independent' of instances somehow?
The defederation thing just led me to making accounts on different servers. Jerboa allows multiple accounts, so I just use the different instances to split the communities I subscribe to by theme. Science for mander.xyz, tech and dev on programming.dev... It keeps my front pages organized.
Mostly it doesn't matter for the person using it*, so you can just pick one that isn't overloaded to start. But...
Ways it does matter:
Your instance's moderation policy and actions. (including what content is allowed/disallowed, how they deal with harassment, etc.)
Server reliability. This can change drastically if a lot of people join at once, as many Lemmy sites have discovered this week! (I believe Lemmy.ml and Lemmy.world have both upgraded their hardware in the last few days to deal with this!)
Admin reliability. This is harder to tell up front, but it's worth taking a quick look at whether the admins seem to be active and responsive, whether they seem like they're in it for the long haul or if they're experimenting, etc.
Switching is sort of easy in that all you have to do is create a new account somewhere, and you don't need to tell your followers because Lemmy doesn't have user subscriptions (though someone could follow you from, say, Mastodon)...
...but it's also not easy in that Lemmy doesn't have tools to export/import your subscriptions (yet?) so you have to add them to the new account manually. And moving your posting/comment history isn't something that's doable at the moment, either.
What I did when moving from lemmy.ml to lemmy.world was put the old/new accounts in each others' bios and add "Old Account" to the old one's display name. I'm not too attached to my post history sticking to my profile.
*I think it matters a bit more for where you set up a community, on the basis that an instance focused around, say, history would be a better place to create an archaeology community than one focused around FOSS. Though you might want to cross-post articles about free software used in archaeology!
Aaaand I just read about the situation with Beehaw.org defederating from lemmy.world because their mods were overwhelmed, so that (for now) the two servers can't interact with each other.
Did they just defederate from that one instance, or was it broader than that? Wondering if I can still interact with them from the instances I have accounts on.
Generally, it does not matter that much, I'm a feddit.nl user and I can just read your post and comments trough feddit.nl. That's because the servers are federated. You can really interact in the same with users on other instances, just like users on your home instance, as long as the two instances are federated with each other.
At the moment, it is not possible to fully transfer your account to another instance, though. This is on the Lemmy backlog, so that might be added in the future. You can make multiple accounts, but that is of course not so user-friendly.
As far as I know, the only major instance that you won't be able to access from lemmy.world would be beehaw.org. They might federate again with lemmy.world once there are better moderation tools, or when they feel more capable to moderate the high influx of new users.
Your account is bound to the instance you created it on. You can go to any instance you want, however you'll need to sign up again if you want to browse from say, kbin.social, instead of using lemmy.world. Regardless, you would see the content from both because they are federated together.
You can view and interact with Beehaw directly from your .ca account. For example, you can go to lemmy.ca/c/technology@beehaw.org and post/comment, etc. It's defederated from .world, so people on that (this) instance can't anymore.
Each instance will have it's own rules and has the capacity to include or exclude other instances.
For example, you want a work friendly instance that does not index NSFW, gambling, drug use, or hate speach. Chances are that you can find and join that instance. You'll see posts from instances that aren't blocked and your posts will be shared with instances that have not blocked yours.
If you want to switch, then you need to create a new account on the new instance. You can maintain accounts on both instances, but they would be separate accounts.
Additionally, if you want to be ruler supreme, and are willing / able to do the tech work, you can set up your own instance that only you and those you invite are able to join. This instance would join the Federated community to share content based on settings.
I know instances can block pulling in content from other instances, but I am not sure if they can block broadcasting content.
You get the most flexibility by hosting your own instance since you get access to all instances and all communities and you won't be defederated from unless you act in a toxic way.
The only draw back is that you have to subscribe to each community individually since you won't have a "local" timeline, especially not one as populated as lemmy.world.
But if that's not a problem then self hosting, or the next best thing, choosing a small non-polemic instance is the way to go.
Having easy migration between instances seems like table stakes since the ownership model means that any instance can prevent you from accessing another if they drop federation
At first I thought you could only have one federated account because beehaw registrstion page wouldnt process but I think they've just been flooded with requests.