1. Razortusk feat, because the Sacred Tattoo alternate racial trait and the Fate's Favored trait give you a +2 bonus to all of your saves. But a Ring of Rat Fangs is better than either, because it costs 5,000 gp, which is worth less than a feat.
2. No, all of your attacks are primary unless the rules say otherwise. There's no set limit to the number of primary natural attacks you can have.
3. Okay, some information:
Magic Items:
Ring of Rat Fangs (see above) - bite, permanent, 5000 gp
Helm of the Mammoth Lord - gore, permanent, 8500 gp
Animal Totem Tattoo (eagle shaman) - bite + 2 talons (they go on your feet, so they stack with claws), 5 minutes/day, 12000 gp
Wyvern Cloak (but it's quite expensive) - sting, permanent, 78600 gp
These magic items are the best way to get more natural attacks, but specific items such as these are often unavailable. If this is the case, I would suggest taking the Wild Stalker archetype. In fact, I would suggest taking it either way, as long as it fits with your character concept. It technically stacks with Shapeshifter, because it only replaces the combat style feats, it doesn't actually replace the combat style that Shapeshifter says must be the Natural Weapon style. In fact, you can still take Aspect of the Beast without meeting the prerequisites, if you really want to. There are lots of great rage powers for this: Beast Totem line for claws and eventually pounce, Animal Fury for a bite, Lesser Fiend Totem for a gore if you don't take Beast Totem, Lesser Abyssal Blood as yet another way to get claws.
So, yeah, those are my thoughts on the matter.
