Two Lemmy accounts for my two main groups of interests. Neither NSFW, just different interests. Same two usernames on Mastodon too. Different instances so hopefully if one goes down the other is still ok, but also just because it’s handy being on different instances when there are federation issues.
As far as managing them, I’m mostly on my laptop and always have two users running in my browser so they’ve both just got a pinned Lemmy tab and a pinned Mastodon tab now. On mobile, Liftoff (for Lemmy) and Tusky (for Mastodon) handle multiple accounts fine albeit with a few improvements needed here and there.
I copy paste my Lemmy sub list into a spreadsheet once a week as part of my general life end-of-week tidy up. Export Mastodon stuff every now and then too. Just in case!