If you replace your current shield with a new one while in Zen Form, the replaced shield goes in reserve. Zen Form never discards shields except by breaking them (or using them to pay for an action) or by changing off of Zen Form.
Teachers can inspire any ally, so yes, if they still have the tokens when their turn comes back around, they can use it on themselves.
In the current rules, yes, placing any other obstacle will override a copy or fog in that space. In the upcoming errata, Copies are treated much more like players, and can be on top of Rubble or Fog without issue. I didn't have a note for Fog, but no reason I can't add one - Fog should be allowed on top of Copies, Traps, or Rubble without issue.
Vigilance's Actions are getting a cost increase. I doubt it will stop being strong, but it will be less free.
I do have a fix for Wild Form actually. I found the ability inconsistent in practice, so I've changed two things about it: One, it does something other than give bonus action dice. It's small but useful - at the start of your turn you gain 1 of each Basic token. Two, it has 5 conditions that can be met to give bonus dice, although it can only give +3d6 even if you meet 4 or all 5 of them.