I think a strong portfolio helps regardless of the track you decide to take. You have plenty of time to work on one, but it might be a good idea to think about taking a class or drawing/photographing/painting/etc. when you have free time and see where it goes. From my understanding, the portfolios are more a presentation of the way you express yourself and therefore the portfolio as a whole should be representative of the way you approach free space. you can fill it with whatever you want and can organize the content any way you choose. In short, the portfolio its self should be a work of design; what goes inside helps describe the overall portfolio.
sounds like you've got some great work experience, so keep those relationships alive and ask for recommendation letters when the time comes. sounds like you're on the right track though. Good luck!