1- "If a bag of holding is placed within a portable hole, a rift to the Astral Plane is torn in the space: Bag and hole alike are sucked into the void and forever lost. If a portable hole is placed within a bag of holding, it opens a gate to the Astral Plane: The hole, the bag, and any creatures within a 10-foot radius are drawn there, destroying the portable hole and bag of holding in the process."
No specific disclaimer is made about a bag of holding in a bag of holding, though I've house-ruled that the total weight in the exterior bag is equal to the actual mass of the items in both bags and can't exceed the limit of either. I use the same rule for all extradimensional spaces since the quoted rule is actually intended to stop characters from gaining too great a benefit from storage devices.
One way around this is to have a Heward's Handy Haversack filled with Gloves of Storing. Gloves of Storing aren't based on extradimensional space.
2- Cloak of Resistance is a resistance bonus; I don't know what a vest of resistance is by the books, since I couldn't locate it. Assuming it's also a resistance bonus, they don't stack. Thus, wearing a +1 Cloak of Resistance and a +1 Vest of Resistance yields a +1 bonus. If the Vest is not a resistance bonus, then they stack.
A ring of protection is a "deflection" bonus, so the name isn't necessarily the definition of what type of bonus it is. Like bonuses don't stack except in certain very limited cases*.
3- Good clerics can't cast spells with the Evil descriptors. Vice versa. Same for Druids. See the individual class descriptions.
Hope that helps,
Greg
* Dodge bonuses stack. The armor bonuses from a shield and from armor stack. Enhancement bonuses on projectiles and projectile weapons stack. Circumstance bonuses from different circumstance bonuses stack. I think that's all.