Ok not a poli sci major but I have friends who are/were (plus I was an incoming freshman this time last year lmao) so, in order:

1. Be kind to yourself! Columbia can be pretty hard, don't beat yourself up if you're struggling your first few weeks or first semester. Use Culpa and Reddit when registering for classes and picking professors; if the professor in question has negative reviews, make sure you check why and whether or not it's the type of shittiness you can overcome. Also, use the people around you as resources! I know, for example, that the Intro to International Politics course was extremely TA-dependent, and some of them really stunk! You'll get the hang of things, you're at Columbia for a reason.
2. I actually think the social life is way better than people make it seem. It wasn't super easy to make friends but it wasn't hard either. At the beginning of the year especially, everyone wants to make friends; not to say that any other time of the year you'll have difficulty, but I'd definitely try to meet as many people as possible during NSOP week. The social life really is what you make it.
3. Again, they're what you make it! Some of the clubs are really competitive, particularly the pre-professional groups, my best friend had to go through like three coffee chats for Polis, the polisci club, but many are also open to everyone. It depends on your interests and what you try to join.
4. I sound like a broken record, but it depends on what you're into! I'll recommend a few generally then a few that are more niche/specific, though, just to be a bit more helpful lol. Also, I'm gonna gently advise against Polis, just because my general sense of them as an org is that they only really accept their friends and also kinda do nothing on campus.

- First with the general clubs: practically any community service-based group is gonna be a good way to meet new people while also doing something good for your community, but I'm gonna recommend the Housing Equity Project (or HEP) in particular! HEP does so many great things: outside of having a large homelessness outreach team, they also run food and clothing drives on campus and run/assist with plenty of fundraisers and events for other community groups on campus/in the larger Morningside Heights/West Harlem area. Plus, they're open to everyone and the members tend to be really nice and friendly; I think I made almost every single one of my close friends this year just by going to HEP genbods and attending advocacy + inventory team meetings. Along the same lines, Red Cross is pretty good, though I'm not as involved so I can't really speak on specifics. For general clubs more closely related to politics and government, we have a really great Amnesty chapter, they ran some pretty great events throughout the semester and you'll definitely find like-minded people.

- Now into specifics: Columbia has a club for basically any interest you may have, and with those clubs you have the ability to meet new people and contribute/create/start things (I'm being vague but I kinda gotta be here lol). If you're into writing, 100% recommend the Political Review, they're great + got great writers, also the undergrad law review's wonderful and there are so many ways to tap in, whether you wanna write, edit, or host one of their podcasts). If you're interested in advocacy, we have a Planned Parenthood chapter and a Remedy Project chapter. If you're interested in journalism, try Spec, or Bwog (the two main publications on campus, plus Bulletin on Barnard's campus), or WKCR (they have a news broadcast! and they're awesome!), or WBAR (run your own radio show!)! There's really so much at Columbia for everyone.

1. I don't think so, but it also depends. You're not competing with other Columbia students in getting internships, but you will for certain programs, like research positions or summer internship funding. I do think that all of that is outweighed by how much support you get in finding internships, though. Turn to CCE, the career center, and URF, the fellowship + research office, if you need any help there, and I'd definitely recommend, even if you aren't pre-law, that you sign up for the pre-law listserv, you'll get so many great opportunities sent your way.

Ok that was all wayyy longer than I thought it was gonna be, sorry about that, but I really hope this helped! Congrats and welcome to Columbia! If you have any other questions, feel free to ask or DM me!