Some questions about 3e exalted rules.

So I've been reading through the exalted rulebook and there are a few things that I'm still slightly confused about.

How does the lore ability work now? It's description states that when you chose it you need to chose the subject of their characters education when selecting it. Does that mean it works like the craft skill? with the character having multiple lore skills?

like for example. Lore:2[Farmer] and Lore:1[Dynast education]?

Or does it mean that they still just have a single lore skill. But that their knowledge starts of very focused and grows in width as the skill increases/they gain specialties?

Also, how does the charm Heaven turning calculations interact with the lore skill? The charm's description say's it requires the characters background to reflect intense mathematical training. Does that mean that anybody who doesn't take lore:[Mathmatics] can't pick this charm?

Makes me wonder why people wouldn't always pick lore: Mathmatics if they can. otherwise they'll be locked out of a charm that looks fairly useful.

And a question that's probably slightly easier to answer.

If you activate a charm that has a duration of infinite. Are those motes/willpower used to activated committed for it's entire duration?