Pixelfed/Mastodon/etc sort of work with Lemmy, in that they can see Lemmy posts. Lemmy can see posts from them if you tag them appropriately, which rarely happens. They only sort of federate properly. And yeah, Loops is like TikTok for the Fediverse.
I’m not saying PieFed is better than Lemmy, just saying that apart from Lemmy, your best option is probably PieFed atm.
I have multiple accounts, but only really for moderation purposes. Cross-instance moderation is semi-broken, so it’s easier to do it that way. Other than that, having an alt is useful in case your main instance goes down.
I wouldn’t generally worry about impersonation, if someone tries it you could contact the admin of that instance and they’re generally pretty responsive.