I think themes are good, it shows you can organise your work.
Avoid photo corners for this. Use photomount. They're alot better and do not leave unsightly corners. Mark out lightly with a pencil where you want the image to be within the confines of the black paper(use the really dark black ones, not the faded black ones which are el cheapo).
Measure twice, paste once. Sometimes if you're confident of your handwriting, you CAN write by hand BUT since this is a portfolio, try not to. It's one thing to experiment but now's not the time. You'll have plenty of opportunity for that in the course of your studies.
Since it's just a basic annotation, use a san serif(eg helvetica, frutiger, gill sans) face. Take note that gill sans while nice and extremely humanist, has a problem in that their small letter L, number 1 and capital I are all just a straight line. You might wanna avoid that face if your annotations consist of numbers and text. Instead, use something like frutiger or even helvetica neue if you can. Standardise your typographic style and faces. Very important but often overlooked is that numbers appear larger than alphabets even at the same point size so you might need to knock down the type size of the numbers by approximately 0.5 points.
