Hi there! From what I've seen in the past years, the biggest/most popular cosplay groups have their meetups on Saturdays, sometimes Sundays. Expect a lot of popular meetup overlaps on Saturdays especially. Disney usually has two meetups, for main and extended which are usually on different days, so you could most likely attend both SU and Disney gatherings~ As for the others, it's mostly first come, first serve for time slots. Saturday is the most popular day, also the day the most people usually attend, so it will fill up first. When it gets closer to the convention date and the threads start appearing for your said interested meetups, check out when they plan to request a time slot! You can always ask for them to move it, though this request isn't always guaranteed. The past two years I think there has been a meetup for all the other cosplays you mentioned, but could be one right after the other some days (I know this problem all too well and it forces me to choose between cosplays since I can't change that fast out of most of mine). When in doubt, always ask! Some other people might be in the same boat and want the specific gathering at a later/earlier time or even on a different day. About a month or so before Fanime, there will be a pinned thread from one of the admins that will list the current gathering times/dates/places as they are received through applications. But always make sure to check the day before and day of gatherings. Several times I've had the location or time change on me without any big announcement, so be sure to check the info desk's master list just in case! Mainly I would say just be prepared if you can't go to one or more gatherings for your cosplays, and always come a little early! (Last year, I missed all of my gatherings due to being just a few minutes late, having times change on me, and just how long it took to walk there from the fairmont TwT don't be like me!)
As far as panels, there is usually at least one SU panel and a WTNV panel. If you are interested in a panel for your other fandoms, do check out the thread I posted about panel requests in the panels group and see if anyone is interested in hosting one, or even if you would be interested in hosting one yourself! I feel like a lot of opportunities are missed at conventions because people aren't sure what everyone else is interested in, that's why I put up that thread~ Basically just keep an eye on the threads here as it gets closer to fanime. A lot of stuff won't come up until around February I've noticed. Good luck and have a great Fanime 2017!!!