Sorry for not completely answer all your questions
For 3), You can give him a fishing rod, knife, and slingshot. I think slingshot is the best item to give, judging from the dialogue.
For 5), I'm not sure either, since I wear it for 14+ days and it does not trigger any special event.
Edit:
For 1), I think I learn how to make Energy drink and Energy drink (Strong) after I found graple in Forest path.