Each of your wounds has a colour associated with it, about how fast the wound will heal. Dark red wounds will heal very slowly, dark green will heal quickly. When you get sage healing, it changes the colour associated with the wound by a little bit, but there is a limit to how much better the sage can make it, and it is different for different injuries. For example with frostbite, the best you can do on your own is yellow, but the sage can make it olive green. You'll really notice the sage's help if you get poisoned. If you visit a sage immediately after getting deathly poisoned (it'll say deathly poisoned, not just poisoned), you can survive 1/3 of the time by getting the sage to heal you until the colour stops changing. You'll have to stay in the village for a few days and get multiple healings per day.
I haven't tried it, but flatbread is probably sufficient, since it's the only kind of bread you can make without modding.
Don't know about the spear, but I guess it would be calculated as decent because that's what it was worth when you gave it to him. One way to test this would be to wait until the last day, give him a spear, see if he is happy to keep stuff, then get into a fight in which his spear degrades (this might take a few companions to arrange), and then see if he is still happy.
Only the act of blocking reduces the weapon's rating. Animals can't block, they can only dodge so no matter how you use your weapon against animals, it won't degrade. If your dodge skill is lower than your weapon skill and you are getting injured, it is worth it to block instead of dodging. Better to ruin your weapon than to lose your life. Metal weapons degrade too, but more slowly. A handaxe can do a lot of damage against a wooden club, so your club will degrade quickly. I think wood can't degrade metal at all, but metal can degrade metal.