Seniority itself doesn't play any role at this point in your life, worry about that when you are with the airlines. Another option, if you had the money - would be to use the summer to fly and earn your ratings. If you flew and studied like every day you could get a lot of stuff done. You could even start in the spring with flying.
I go to school full time and instruct during the summers. Depending where you work, FBO's get the most busy during the summer months and could use summer only CFIs. I get about 300 dual given a summer and teach ground schools as well.
As far as being an instructor while going to school, don't recommend it because you will not be available for your students when they need you and probably wont do as well in school.