If your fan noises 😉 are really loud you should install a wall made of acoustic drywall in front of that shared wall and fill the gap with acoustic foam. Acoustic foam alone won’t help with loud noise. Since that mostly reduces the reflection of sound. Sound can still pass trough the foam and then trough the wall.
The Metal Gear series is interconnected to a high degree. Sure the games are perfectly playable without playing the previous games, but you’d miss a lot of plot points. Like for example even the PSP games are pretty vital to the story. Because several characters of Peace Walker show up in MGS5 without much explanation of who they are.