So Ragnarok Disasters are 100%? So they're basically 80 AP to host yourself. If you put in four hours of AP daily, you'll get enough pieces for 20 Regalia per month I guess. Plus 30 from founding them. And you can work on multiple elements too, I guess. I wonder if there's a daily limit past the 3 for Experts...

... sounds a bit too good to be true, to be honest. I doubt it's 100%.
The fights themselves are probably pretty tough, Thunder has 15m HP. The rest have even more. For comparison, next Raid event Ragnarok has 9m.

Anyway, rough expected schedule:
Thunder: January
Wind: February (or never since we already had this patch)
Fire: April
The weapons themselves: April (and if I recall right, only Arthur and Dartagnan were available at first?)
Water: May
Light: June
Dark: October?

So, Wind will have a huge head-start from Water. You don't really need to decide anything until May 2018.