A question for the MGS fans.

No, it's by far the weakest story, and you would only miss context for a couple characters. I recommend playing 3 first then Peace Walker.

Not exactly a necessary requirement to understand Phantom Pain.

The previous games give you a canonical backstory about the protagonist if you're interested in that.

You don't need to play all the previous games for that as you can peruse from the innumerable YouTube videos that portray the MGS lore in a varied level of detailing whichever suits your need.

Just watch one of the many many story summaries (up to Phantom Pain) and you are covered. Like this one

Don't worry about it. You could play all the MGS games and not understand anything.

I think you should play/watch Ground Zeroes maybe, other than that. You don't need to play the other games, although context always makes games more enjoyable for me.

Although not being a fan of MGS, you might enjoy 5 more than MGS fans because of reasons I won't say cuz spoilers.

You could always read the plot summaries of the previous games on wikipedia or somewhere. It's probably not worth playing the actual games unless you're interested and have access to them, although I hear they are great games. I still have nightmare flashbacks from the playstation when I got the game over screen but they were only lying and I had to keep fighting in that tiny preview window in the corner, or when I had to switch controllers to the other port to beat a mindreading boss who suddenly couldn't read my actions because he was reading them from port 1. So I'm good with just reading the synopsis, thanks.

Recently i finished MGS1, 2 and 3. Today i will start MGS4 :)