Actually on the LIRR side, you have two choices for escalators going to the LIRR ticket areas. One was already described which is on 34th just before 7th Avenue on the SW corner. The other is on the 7th Avenue and 32nd Street right at the entrance to MSG. You take that one down and then turn right for a second elevator which takes you the LIRR ticket areas.
As for elevators/escalators, there is no uniformity of location so since I don't know from which track your train will depart, I really can't help you. I don't have tracks 13-21 memorized.
That said, when you get to Jamaica, you'll have escalators available to you. Just sit toward the front of the train (on the 7th Avenue side).