FF newbie, plenty of dumb questions inside

MrsHK

So this weekend we'll probably need to start supplementing with formula. Due to my low supply we'll have gone through my freezer stash we've been using to supplement. (Please this post is about FF, not my supply, I've already covered that topic plenty).

DD is our 3rd baby but I have no experience with formula so here are my newbie questions:

1. If DD gets formula does that mean she doesn't need the vitamin drops? Are they just a BF thing?
2. Tips for preparing? I figure I'll mostly just be doing a bottle at a time since it'll only be supplemental (for awhile I hope). Do you just shake it in the bottle? Whisk it in pitcher?
3. Does it have to be refrigerated? How long in advance can you prepare it? How long can a bottle stay out?
4. How do FF diapers differ from BF diapers?