Play in release order!!!!
Buy MGS1 from the PSN store or you could watch the cutscenes on youtube if a PS1 game is a bit outdated for u
Buy HD collection
Buy MGS4 used for like 5-10$ (its available digitally now on PSN as of last week for 19.99$)
Pre-order Phantom Pain
Done and enjoy
Btw how much do you know about the general story? like you know the Snake in 1,2 and 4 is a different person then the Snake in MGS3,Peace Walker, Ground Zeros and Phantom Pain?