Mastodon has partial account migration (mostly a redirect), I don't think lemmy has that (yet?) although both are built on the activitypub protocol. Either way I hadn't used that account for long and didn't care enough to keep it.
Best way to have active accounts is to avoid lurking. I've found myself falling into the trap where I act like I'm on reddit or YouTube and I don't want to give them free user engagement. The exact opposite of Lemmy.
In my opinion, people don't mind hearing what you have to say. I wouldn't call an upvote content. So I think comments and posts, if you are feeling daring on any given day, make for a better experience and let's people be more social.
Basically, if everyone says something and interacts, this place will feel a lot more lively.
I had 2 with 250k+ back in the day. Sequential accounts, rather than them existing at the same time. I 'retired' a long ass time ago and mostly just lurked on communities that interested me. I came over during the migration because fuck spez.
I post a shit ton here; not because I care about internet points, but because Lemmy was pretty small and needed content when I joined. All of my stuff I post stems from my group chat or from memes I stumble across on non-reddit related sites.
I really like sharing memes and shitposts with my friends so I do it here too
I only ever started a second account on the old place (after 13+ years) because I got permanently banned from two subreddits that I wasn't quite ready to give up completely because they gave me no option to appeal.
Then these account will not be monthly active. A more fitting example is probably a porn account (don't accidentally post nudes on lemmy, people!), a troll account, a serious account, and the ten other accounts to upvote everything on the troll account.
I definitely had 3 because I forgot my login information for an instance and just made a new account because I don't care. Not seeing Hexbears on my current instance is a plus.