Good to see Lemmy grow, but I hope that the decentralization will work out so that the large influx of new users will spread out as evenly as possible. General purpose instances help balancing the load, and last time I checked join-lemmy.org there have been several general purpose instances, which seems promising.

I assume that there is something that is O(N), which explains why wait time scales with community size (amount of posts, comments)

Just looked. First 1/2 loads were slow but after that it's lighting fast! I think by not everyone establishing a Websocket connection and just loading once performance should increase a tad bit.

Maybe Guides / Information could be shown on the lemmy web frontend by default to lower the entry barrier?

You can also try installing the PWA (if your browser supports it). On https://sh.itjust.works, Somewhere on the browsers web page options, there should be something along "Install" or "Add to home screen". PWA is basically the website but without browser controls, so it feels more native.

Lemmy also has an API that clients can get information/content from. The Web frontend (lemmy.world) is one of them. Apps like wefwef and Jerboa also ask the Lemmy API for content and display it in their own way.

Element is a client for Matrix, a decentralized chat protocol featuring end-to-end-encryption. Lemmy seems to support DMs over the Matrix Chat protocol. Matrix is federated, so user1@matrix.org can talk to user2@matrixinstance.space.

Some fediverse apps can work together seamlessly, some can't, and support seems to be growing over time. E. g. Mastodon users can comment on PeerTube, but Lemmy users can't (not that I know of), but it's not impossible that will change in the future. But, kbin for example integrates seamlessly into Lemmy.