Perun
Mushroom
Maybe raging should prevent the use of heavy armor...
It does. You can't rage in heavy armour. And (although it wasn't mentioned), increased movement (5th level, IIRC) also doesn't work in heavy armour.
I am more worried about dipping moon druid level 2 and will certainly rule that at lvl 2 you only be able to change into a 1/2 CR animal.
I was looking at statistics of certain animal forms, and while attacks can be pretty impressive, especially at 2nd level, the AC tops at 14 (dire wolf, giant hyena, IIRC). The most plausible animal form (you have to have seen the animal to wildshape into its form), brown bear, has AC 11 and 34 hp. While it might be good (or even too good) at 2nd level, it will soon fall behind, esepecially for someone with just a 2 level dip in druid.
OTOH, limiting wildshape to CR 1/2 at 2nd level seems like a really good house rule. Plenty of good combat forms at CR 1/2 (ape, black bear, giant goat, panther, giant wolf spider, etc.).
Regards.