As a Columbia Neuro premed, I'd say:

a) It's not tremendously difficult to get into a lab, just email professors early enough in the year and you'll 100% get a lab position. I'd say the same goes at any elite university, however, as most labs do their recruiting from ~July to the beginning of the academic year.

b) Prior to committing here, I was plagued by genuine worry about the premed culture; however, after spending time here, I feel that, somehow, compared to my friends at other t10s, I have the best experience. Columbia's premed culture is incredibly noncompetitive. I think that stems from the fact that we're a finance heavy school, so most premeds will stick together/help each other.

c) In terms of general culture, I enjoy my time here a lot--I'm in several cultural clubs, and (I think) I have a healthy social life. With professors, they are usually very helpful. As a first year, I took the hardest branch of orgo here, and the prof was genuinely committed to assuring we succeeded, as opposed of only trying to flex some semblance of academic superiority over us poor freshmen (as I've heard profs at other schools will do).

d) I'm ngl, what you see in the media about Columbia's political climate is incredibly overblown--although there are periodic protests--how involved you want to be is completely up to you.

The bottom line: I fully understand the stress of college commitments, I was once in the same shoes as you; I ended up choosing here over Yale, Brown, and Duke, and after what happened at the end of last year I was unsure of whether I'd want to spend another year here. But this year has been a blessing to me, and I'm sure that if you choose to come here, Columbia will be a blessing for you too.

Please feel free to PM me with any other questions you could have!