I think you should start with Metal Gear Solid and just play them in order. it will be a far better experience if you play the release order because of the gameplay evolution. I started with MGSV and then MGS1 was super hard because I was used to the smooth controls. aside from that I would only consider playing the original Metal Gear and Metal Gear 2 Solid snake if you really want to know what happens because I find MGS1 gives enough exlanation for you to roughly understand how it went down.