Im joining in on the reddit ditching thing, and was kinda worried at first that i wouldnt be able to like use it the way i did reddit as it feels like a whole new place, but after engaging with posts and people and actually being a part of lemmy rather than being lurk mode all the time i was pleasantly surprised with how easy it is to become a member of the community, theres a reasonable amount of subs (or whatever the other word for em is) that fit my interests, enough linux content and shitposting for my liking, and the overall random posts made by people equally fed up with Leddit. (also i admit i used reddit a little cus there was this post on the fedora sub showing how to fix a sound issue i been having after a recent update)
It's fine, but it's a pain having to create multiple accounts when some instances aren't linked to the one you picked to create an username.
For the rest I think the other comments have already pointed out what would need to improve in the future if we expect to leave Reddit; curiously, most of the problems we have here are the same or similar to the ones while trying to use Mastodon.
Yes, if a community is inside an instance that isn't linked to the one where you registered then those won't appear inside your search and you won't be able to subscribe to them, if you want to subscribe to them you have to create a new user inside an instance that can communicate with it... If that's not how it's supposed to happen, then I found a bug
Almost all instances are linked. If it doesn't show up the first time you search it just means it hasn't been cached yet. It'll show up after you wait a bit and search again