I think that it wouldn't need matting at all. I think either a nice silver frame or just straight sleek black. I'm going with silver...not shiny silver though. I think that it will bring out the color that he used for the names and framing of the pics. I think that matting would be too much as the poster is quite....busy is not the word that I'm looking for...but, you get my drift, yes?
I have a few poster frames that I bought when a local poster store was going out of business. I just have a shiny black 1.5" frame around the edge. It would work well except that it's only 18x24 and I bought a 20x30. I'm going to try to find one like it though.
I think my poster will have its own accent light with a milk painted, rustic window frame. I think that something with a bit of history and hand made would go well, rather than something manufactured.