Hey! This is actually the current final edition, next one I would make would be 2nd edition of the game (that would be closer in rules to WARDEN, the spiritual successor), if I ever get to making it. Thankfully, WARDEN has an editor and has had much more time to brew.
I am aware (and a little ashamed) of the state Pathwarden was left in, but what is done is done.
On the examples, I am not great at writing examples, I must admit, that's why they are so sparse. Discharge, for example, is meant to lower automatically, but you CAN lower it with an interact action, as well.
I'll answer the more exact questions as well:
1) Focus items don't grant the Cantrip, that is the benefit of learning the spell. I think that is implied by the rules.
2) Yes. That simply makes sense, sadly the rules don't imply that.
3) Spell Difficulty is just 10 + Magic Bonus
4) Yup, you got it.
It's honestly kind of ironic how the next game managed to fix basically all of these ambiguities more or less, and I'm releasing the 0.3 version which is pretty close to final, in a few days. It also has a better layout, and editing, and everything. It's very hard for me to recommend Pathwarden again before I make a leaner, cleaner 2nd edition that is closer to the ultimately much more superior mechanics of WARDEN.