Just begining with the game and i've got a couple of questions...

When you use boons to get a critical wound, are they expended or you can count them anyway to to obtain other benefits from the action card? For example: I've rolled 3 boons, can i trigger the critical wound with my sword AND perform a manouvre for free with my "Melee Strike" (2 boons required)? or i must roll 5 boons to do that?.

The traits listed under the name of an action card entail some form of restriction on when purchasing these cards? Any character can buy a "slayer" or a "way of the sword" card without having a trollslayer or a Swordmaster career for example?

You'd need 5 boons to get both the effects you're talking about. You can't reuse boons like that.

The traits are just for reference and don't impose restrictions. But, fwiw, as a GM I'd be inclined to restrict their use under certain circumstances.

Thanks for the answers monkeylite! (on both topics )