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?
What does defederation imply? Feeds aren't aggregated, or users are not allowed from the other instance?
Iirc no activity from one instance is available on the other. No posts in their communities, no posts/comments from their users.
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?
The fediverse is a group of social media platforms that use the active pub protocol to pass along user interactions between instances (servers run by different people).
Lemmy is the reddit of the fediverse, meaning posts in communities and comment in a trees structure.
Kbin is also the reddit of the fediverse, but with some less features (manly on the moderation side). Because they both use active pub in a reddit style they can easily interoperate.
Mastodon is the twitter of the fediverse meaning their content (mircoblogging) doesn't fit the lemmy format but you will only sometimes see some posts like 'If you can read this I have managed to post from mastodon to lemmy'.
Is there a way to easily see which instances are defederated from others (or conversely which instances are connected)?
To add to what others are saying, there is a list that may be helpful. Let me explain it a bit though.
The list below shows various Lemmy instances in a table. An instance can block another instances (this is what they control). The instance can be blocked by someone else (which they can't control). Either way, a block is in place so the two cannot communicate.
The column header BL specifies how many instances they are blocking. The column header BB says how many instances are blocking them.
If they have a high BL, they likely do not want to federate with many other instances which can be a drawback. If they have a high BB, that instance is likely acting in such a poor manner that nobody wants to interact with them. Basically, you may want to reconsider instances which have an excessively high BL or BB.
Note that there are pretty bad places out there so having a BL of 0 can be an issue as well. A BB of 0 may indicate that an instance is very new so nobody really knows about them yet.
The list is sorted by how many users are at an instance. If the instance has a high amount of users, the service is likely a higher quality service that can grow over time. Small services aren't bad per say but they may eventually disappear or overload if too many people join them.
Like most things, this is just more information to help guide you in your decision making. The best decision is one that you make on your own after you do your own research.
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.