The only thing I should warn you about is that Kojima tends to retcon his history in games a lot. The version of MG1 and 2 mentioned in MGS1 is slightly different and MGS1 tends to have Snake recall events in MG2 in a very different manner than what actually transpired in the game.

MGS3 practically retcons the entire chronology given in MGS1 concerning events about Big Boss.

I'm still in the process of playing Portable Ops for PSP so I can't make too much recommendation in regards to story just yet but it has introduced (and once again, slightly retcon) the history of a few key characters from the later installments. From the way, Kojima has been talking about it though and how the trailers appear, it seems like Peace Walker will play a significant role in the series long and twisting story.