Nice overview but I'm not sure I completely agree with you on everything.
If I want to make a community, is there a reason I would choose one lemmy over another?
There's absolutely good reason to choose instances wisely when making a community. Some instances defederate from others, and you want to make your community somewhere where you agree with the moderation policy. Also, it might be easier to immediately reach people on a larger instance.
If you create your community on lemmy.ml, you might not reach everyone because some people and instances have blocked .ml due to different philosophies. If you make it on Beehaw, you'll reach fewer people as they have a higher moderation standard than most, which could of course also be good for your community. Lemmy.world is more neutral in their moderation policy, but I'm sure there are pros and cons there as well.
I like it when there are specific instances for specific niches, as it gives the community control over who to federate with. But of course, that's not always possible.
If I report a comment, is my report private?
They're not public at least. Few things on the Internet are truly private.
Some instances defederate from others, and you want to make your community somewhere where you agree with the moderation policy.
Is there a way to easily see which instances are defederated from others (or conversely which instances are connected)?
What does defederation imply? Feeds aren't aggregated, or users are not allowed from the other instance?
Also one other major question. I thought lemmy was its own thing, but I guess it's part of the Fediverse? The Fediverse is just a set of protocols? What is lemmy then?
No, this is because of already many abuses, the local admins / mods and the "origin" instance admins / mods can see your name.
Are the powers of moderators similar to reddit’s?
Much less but soon with sublinks aw lemmy compatible backend / ui it will become a lot better.
Any other differences from reddit I should know about?
Everything here is PUBLIC, because of federation many things gets federated everywhere even without you noticing sometimes.
Everyone here is unpaid, so mods and admins are here equal instead of reddit admins beeing paid millions for beeing *ssholes.
Here, if you dont like the admin of an instance you can somewhat easily swap to a different instance ( sh.itjust.works, lemmy.today .... ), but be aware if you just went out with a "Bang", like you trolled a lot and got permabanned you wont be welcome in the other instance because the admins are most of the time in good contact to each other, and warn for trolls or harassment.
In an oversimplified way: when it comes to moderation, Lemmy is mostly like Reddit. The big difference is in the administration - each group of admins controls its own instance, with no group controlling the whole.
Where can I find a list of most active lemmy instances?
Here's one. I'm linking this one because it allows you to look for communities ("subreddits") too, not just instances, so it's comfy to use.
If I want to make a community, is there a reason I would choose one lemmy over another?
Yes. For most of the time, it's probably better to create the community in an instance focused on that topic, as people who like it will probably gather around that instance. So for example:
Votes are semi-public. Not every instance makes them public, but anyone who is on an instance that does can see them.
Your comments and posts are public, I think your subscriptions as well, so if you need to protect yourself from harassment the remedy is just like reddit: have accounts that don't overlap, one for politics, one for anime, one for whatever.
You should definitely only create a community on an instance where it fits. For example, a muni about fashion doesn't belong on the the solarpunk instance, and a muni about ocean life doesn't belong on midwest.social. Many instances are "general" instances, though.
Moderation here lacks the robust toolset of reddit, so it's hard to compare them. But you can have posts and comment threads removed (lemmy removes whole threads, not just the parent comment); you can be banned from a muni or even a whole instance; but no one can ban you from all of lemmy. Unlike reddit, your home instance can be defederated, which is basically shadowbanning your entire server. Defederations and mod actions are public; other admin actions can be done stealthily by directly editing the database.
You don't need an active "home" instance if you have a robust subscription list, honestly, because you can subscribe to munis on other instances.
In my opinion, the major difference between instances is moderation practices. There may also be technical aspects such as down time or frequency of updates that may affect your experience.
I find that lemmy.world has well balanced moderation. They don't allow spam or abuse, and they're not pushing an agenda.
Depends on what you're looking for. Each instance has a general vibe of user, so while .world may be good for someone, .ml may be good for another, and beehaw.org may be good for another, and so forth! .world is generally a generalist instance, but ironically because people with more specific interests are already on more specified instances, .world is more likely to house people that don't fit well into other servers, paradoxically creating a type and it's own unique vibe.
.world is a good general purpose instance for just about anything. I think it has the biggest population at the moment, so communities there are likely to get at least some engagement.
For "general discussion" it doesn't really matter. The instances are federated so you'll likely get general discussion in comments from lots of people from lots of instances anyway, wherever your community is based.
Some people get almost nationalistic about their chosen instances or have grudges against people from certain other instances. There's sometimes inter-instance politics with some servers defederating with others or threatening to for various reasons. It's kinda fun to watch in a popcorn drama kind of way. For the most part, the instance doesn't matter.
Others have already answered, so I'll just add to it: the decentralized nature and lack of a profit motive help keep it from going downhill like Reddit did, but at the same time this nature attracts a lot of leftists and tech enthusiasts, so Lemmy overall definitely leans in that direction more than Reddit does.
People actually reply to your comments and upvote/down properly, which makes actual conversations and healthy discussions posible.
That for me is enough to keep me engaged in this site instead of reddit. It also helps that the majority of users here are real humans and not bots farming Karma, pushing agendas or promoting some shit.
As everyone has given proper answers for all other questions i'll answer this one . No here moderators come under admins and that wasn't a thing on reddit.