Starting your portfolio already in level 4 is a good idea. You can then collect and add the best projects, sketchbook pages, videos, blog links etc - and add to your online or hardcopy portfolio.
Format is key - online - it can be any size (within reasonable file size, of course) - actual carry-around-portfolio should be of a manageable size. A3/A2.
Don't cram the portfolio with unnecessary work, it should be a collection (archive almost) of your best work, that shows the all-round skills that you are expected to have for employment, internships, work placements and education purposes.
Make sure that the work is neat and tidy - bound, mounted on good quality board or just a set of crisp, clear printed pages. You can make the portfolio into a 'book' format and bind it together into one. You can use a traditional portfolio case with plastic protective sleeves. It's up to you. Your 'design eye' need to consider what will work best.
Add a CV - don't give away personal details if your CV is posted online.
Make business cards and add your blog/website to the card. Make sure your email address represents you professionally. No silly email addresses.
Always best to include
Contents Page
Introduction (a brief 'hello' from you, about you, your background, your skills and what you hope to achieve etc)
Annotation for each section (information about particular projects and what your role was etc)
Awards, nominations, participation in live projects etc
References
