You can do a few deals make some cash then get your license..This makes the most sense and I recommend this strategy to my students.

I'm the least familiar with this profession of the three. 

My medical resident recently up and left saying his student loan payments just ballooned and he could no longer afford the rent. 

Consider student housing see below.Locate and attend 3 different local REIA club meetings great place to meet people gather resources and info.

However do consider that if you are going to continue to rent to various college students these kinds of situation could and do arise so you might put some wording in your lease that will help your renters manage the use of the building and resolve or prevent common disputes. 

The second factor was this will allow me to completely pay off my student loans and be able to direct that money into more investments.

Your work in education serves and uplifts the minds of your students.  

Take a good look at student housing see below.Locate and attend 3 different local REIA club meetings great place to meet people gather resources and info.

Take a good look at student housing see below.Check out the Start Here page http://www.biggerpockets.com/starthere Check out BiggerPockets Ultimate Beginner's Guide - A fantastic free book that walks through many of the key topics of real estate investing.Check out the free BiggerPockets Podcast - A weekly podcast with interviews and a ton of great advice.

He has student loans which he should have paid off in 5yrs (he puts a lot towards them monthly).