The porfolio seems to me to be an ongoing, continuous activity. I have seen all sizes, so far, from 8"' x 10" to ... I don't know ... must have been something like 30" x 36" - from a a good friend who owned an advertising agency, and used it in sales negotiations with clients.
My own is 11" x 14" - Panodia. At present there are 20 11" x 14" prints in plastic and a *bunch* of loose ones in there. I would *NOT* present it with loose prints.
Given that the portfolio is the vehicle for the fist impression, I am going to be extra finicky about its composition. At present, I have to replace four or five color prints that have yellowed ( more properly, "tanned") over time.
Also, my portfolio is mixed black and white and color - I am thinking of separate inserts devoted to each.
Last, I am going to pay a lot of attention to the size and format ... and possibly, either smaller prints mounted on some sort of archival paper, or overmatting.
Now ... to find TIME...