Dorms are pretty standard. Gropius is small but cheap and social. Hastings and North are significantly more expensive. There's a lottery for the dorms, but I think almost everyone who wanted it got in. I'd recommend Gropius for 1L, unless you really want something bigger and nicer, and/or you have a roommate to split costs with.
There's no "meal plan", but there is a pretty decent cafeteria, and you can pay with your student card so it's more or less the same thing. There's also plenty of places to get take-out within a 5-10 minute walk. There's kitchens in the dorms too.
No one fails. Ever. It's very, very difficult to get anything below a B-. Don't worry about people with graduate degrees - law is a different subject, so I can't imagine they help too much. If you don't follow US news and politics you might want to spend an hour or two on wikipedia learning the basics of the American form of government and constitution, but that's about all you need. Seriously, you will be fine.
From the HLS website: The most important point for an international student is that Harvard treats international applicants exactly the same as US applicants for the purposes of financial aid. Any loans which the US government would give to a US applicant, Harvard will match through its own loan program. This is incredibly generous and unheard of at many law schools. * Harvard does not offer merit-based scholarships. All of its financial aid is based on financial need