1 Not much, but if I say 'during lunch' I don't mean the whole time.
2 It could depend on what comes befgore it, but I would say 'she studies at xxxxx School/College'.
3 Each- can be with two or more
Every - three or more
Often they are the same, but if we want to emphasise the people as individuals, we use 'each' and if we focus on the group use 'every'.
Student or Learner