jointhefediverse.net seems to be a commonly linked resource for directing people to join the Fediverse.
Curiously, it does not list Lemmy under the list of Reddit alternatives. Their GitHub README explains why.
Previous relevant discussion: https://lemmy.ml/post/78808
You can have multiple accounts on multiple instances. In fact, I recommend it. No need to delete your ml account, just keep it as a backup or curate a different feed on it.
I’m way too lazy for that. I don’t even have more than 1 email account. I use the same username everywhere lol…