We can monitor actual active users that an instance has. Anything artificial in volumes enough to have an impact would be noticeable in some way to other instances.
I don't want to shame anyone, but I've had people sign up give me their full DoB and offering to show me their ID. I know of people who disclose their id to get access to nsfw discord communities.
To anyone surprised at this: welcome to the fediverse, please treat everyhing you do or say as public.
The way to achieve privacy around here is by following the long forgotten arts of the old internet before Facebook was a thing: use a Nick name and don't tell strangers on the internet your real identity.
Your home instance will act as a proxy and only they have access to your email and IP address. That does stay private.
So, as long as you trust your home instance to not leak or disclose your connection or sign up data (which would be illegal in EU countries), just sign up with an alias.
A very positive aspects of this is that it should allow us to detect voting manipulation by correlating the activity of certain potentially malicious actors. If Lemmy instances take vote manipulation seriously and do their best to block bots this has the chance to make Lemmy / Kbin much more transparent and credible than Reddit ever was.
If you want privacy on the fediverse, use an alias. It's as easy as that. This is akin to the old adage "don't tell your real name on the internet" which Facebook destroyed.
It's not possible to make votes private is your care about no manipulation happening. Otherwise any self hosted instance could just communicate any made up amount of votes.
I'm sorry to break it to you but from what I've read their federation will be based on whitelists and only federate with very large mastodon instances.
This has been changed with the latest version of Lemmy. Try this link: /c/aviation@lemmy.ml and check over at lemmy.ml/instances to make sure your instance is not blocked. (It's at the very bottom, I just checked for you and it doesn't look like it).
Edit: your instance is using an older version. Searching should still work. Try a couple of times. Make sure the search page is /search and use no filters
There is nothing preventing the creation of meta-communities other than writing the code to put things together.
Using the Activitypub protocol a group is nothing else but an actor that announces ("retweets") every message that is tagged with its name.
To have meta groups you would have an actor that subscribes to a list of groups and announces ("retweets") anything that shows up in its feed.
Currently you could make a sort of meta group by having a bot user account that subscribes to several communities and announces everything it sees. The only problem is that Lemmy doesn't yet let users follow other users or retweet content.
I would hope that anyone doing so would be dealt with by moderators.