But where should I even start?

MGS1 and then go order of release, anyone who says anything different for this series detests art

Which ones are skippable?

Ghost Babel, MG1, MG2, both Ac!ds and Portable Ops unless you REALLY enjoy the MGS stories or peace walkers gameplay, Revengeance probably unless you like character action games

Metal Gear Solid PS1

Definitely the OG one, Twin Snakes is sort of a fine take on a reimagining but it loses much charm compared to the original one

what are some tips I should know?

If you come from MGS1 to 2, you might've never used the first person feature barring some forced gameplay sections or maybe to gawk at the cool artstyle. Use it in 2 liberally. You'll understand.

Starting at 2 whatever bullshit you can think of to do with combining items and systems, the devs likely thought of it. You can just cover-to-cover-sneak and knock out or shoot people, but half the fun is in the odd things you can do

Definitely play MGS3: Subsistence over Snake Eater. The game does work better with OTS view.

Starting at 2, if you feel a cutscene of importance coming up, make sure you have time to actually view them. I think the worst of the worst is MGS4 at 90 minutes. Excluding Peace Walker these tend to be games that aren't really well suited to 30 minute playing sessions

For a lot of later Peace Walker the absolutely most crucial, critical item is the resupply radio thingy. Keep it in mind.

Play MGS V on PC so you can easily load sick tunes in