I made a lot of questions, so I'll give my 2 cents on the subject.
By "encounter" I mean combat, because it's what really matters after in this discussion.
1-Per encounter powers recharge when encounter ends. If characters are attacked by more monster one round after the previous encounter ended, they get all their encounter powers.
1a-I'm really just guessing, but I think 95-99% of the encounters a group face have a clear and distinguishable end. For the other encounters the Bo9S rule of thumb (1 fullround without being attacked or targeted by enemies or attacking enemies), or when initiative counter doesn't matter anymore, or simply use DM's discription.
2-When using encounter powers outside combat, a character can use them at will whenever they could, by analogy, take a 10 when using a skill. So, if the rogue is in a situation he could take a 10 to lockpick a door (not being threatened or under serious stress, etc), he could also use his "Roguish Lucky Kick" encounter power every round to knock down the door.
2a- Maybe there will be encounter powers that are only effective in combat, or can only be activated by things that only happen when character are fighting.
3- Buffs that last until the end of the encounter, when used outside combat. Well, maybe they have some conditions to be applied that only appear when character are fighting, or maybe they are just really useful in a combat. But I have no idea so far.