First of all, if you're interested in Williams, visit the school for more than an hour or two. Do an overnight here, and run with the team. While that's still an imperfect way of figuring out how much you like the school, it's a lot better than just asking letsrun.
As for some of your questions, the team is large––I'm guessing it's larger than pretty much every other college XC team, because Pete loves walk-ons––but is very closely knit. The entry system helps a lot in terms of branching out, and it's absolutely possible to have close friend groups, clubs, or interests outside the team, but the team itself is very close.
Pete's been coaching for over 40 years, and Williams has perennially been excellent on the D3 level. The coaching is top-notch, but don't expect to be told exactly what to do each day. Pete likes to treat you like an adult and for you to be the master of your own training in terms of how much mileage you want to do and what group to train with. If you need advice, he or the other coaches are always available to talk about it, but only relatively rarely will they tell you exactly what to do.
The men's and women's team practices at the same time and has all the same coaches for XC, so we're closer than many other schools. Non-drinkers are absolutely welcome, and many of our top runners and captains don't drink (as well as many of our lesser runners).
We travel overnight a couple times each season, but academics comes first and if you have a test you need to study for or a paper you need to write, as long as you let the coaches know, they're always ok with you missing a practice.
You should do your own research as to whether Williams is the right school for you academically, but we do have many history, polisci, and econ majors on the team. In terms of internships, I assume Williams is the same as any other top school, and probably isn't appreciably different from Amherst, Yale, whatever.
But bottom line: don't trust what I've written here just because I claim to go to Williams. Letsrun isn't the best place to find out about Williams. Talk to the coaches more, do another visit here, and determine for yourself whether you want to go here.