I personally much prefer vim due to its infinite portability (I can use the same editor pretty much anywhere), but it came with a big up-front learning curve that I used when I was ramping up on a new codebase anyways.
If you like VSCode and feel productive in it, you should stick with it. If you're in a situation where you're able to go slower and ramp up with vim, I think that would be a good time to try it out. The end-game is that your vim-config is truly portable, and no matter where you go, you'll be able to easily duplicate your work environment. Also, once you master the motions, you'll be much faster navigating bigger code-bases and can easily work on a server if need be.
It really depends on how they level you, which you won't really know until you engage with them and interview. It's less likely you'll be presenting at conferences and writing articles on what you're doing at Facebook, though not impossible.
Work/life balance isn't as good as other FAANG, but not necessarily awful, though it depends on team. There seems to be good leave and a general support for parenting and family responsibilities, but I can't speak too well since I'm not a parent. If you learn about their parental leave, that should give a reasonable idea of how they value parenting.
If you don't think there's an amount of money you can get paid to not be the "biggest fish", then it may just be worth getting an offer to request a raise at your current company. Regardless of how you feel, I think it's totally worth interviewing with Facebook, to learn about the company and what they value.
I've also worked with people at both FAANG and non-FAANG where the issue is motivation and not "intelligence", so I would frame it to myself as that.
Depending on the company, you might be able to switch sooner once you have your first performance rating. Most FAANG companies try to have managers support what's going to give you lasting longevity at the company, not necessarily on the team.