>>724561676 (OP)
>Should I pay the original NES games or should I jump straight into the first Metal Gear Solid?
You probably meant to say "the MSX originals", no?
The NES port of MG1 is notoriously awful, and MG2:SS was never released on NES at all.
But the answer is: up to you.
If you can stomach some TRUE Retro, then MG1-2 are worth checking out. Especially MG2:SS is a truly great game, and a proper proto-MGS in every conceivable manner.
But if you are at all unsure, and want to bite the juiciest part of the franchise right off the bat, then Metal Gear Solid 1 is the game to start with.
It's still the corner stone of the series' overarching plot, and a great self-contained tale with iconic characters, settings and atmosphere.
MGS1 also has text summaries of MG1 and 2 in its main menu, which you can read first.
I'd also check the "Briefing Files" and try the "VR Training" before jumping into the campaign itself. The former's essentially a set of videos that flesh out the backstory more, where as VR training's a set of tutorial / challenge missions that teach you the basic mechanics. The main game itself won't hold your hand, typical to 1990s' games in general, so reading through the Manual + VR training is the way to go.