I did find all 120 pretty much without help. When I had 119, I did look to see if I had all the shrine quests and found that I was missing one, so that helped a small bit to give me a basic area to search. However, it's definitely possible. Revisit every village/stable and talk to everyone...
If you do need its fang (which I know is needed for some upgrades), you have to get close enough to shoot it in the mouth. Farosh is easier to get because he comes right under Floria Bridge in Faron by the Lakeside Stable. I'm not sure how specific it is, but if you jump and use the time...
Yes, they definitely are. That made finding all the race related ones and flower trails very difficult to find. Some are actually very far away from where you get the "seed" (after Hestu's gift, I'm not convinced any of them are actual seeds). I think it would be best to have each marker on...
I think it's the recipe given in his diary in his cabin, but I never actually tried it and just made food for myself with the spicy peppers. Something to do with peppers, meat, and fish if I remember correctly.
Yeah, once upgraded, I believe the Champion's tunic is the highest defense for any single piece of armor in the game. I just didn't tend to use it much because I wanted armor set bonuses (except for in pictures and before cutscenes because I want it to look genuine ;)).