First two years are probably about half lectures and half small group sessions (maybe slightly more lectures). Lectures are all optional attendance, videotaped, and posted online. Small group sessions are mandatory and generally involve discussing clinical case vignettes. Also, labs are generally in the afternoon and also required attendance. This was how it was when I did it, it may be slightly different now. Most of your patient encounters the first two years will be through the class called Art and Science of Medicine. The first few weeks you will probably learn about topics like professionalism and ethics. After that, you will begin to learn physical exams and then you will have weekly patient encounters in the hospital.
Career guidance was hit or miss when I was a first year. I was proactive and found a mentor who helped guide me. We were all supposed to receive mentors but I don't think this actually happened. There has been a shift of some administrative people since I was a first year, and I believe things are better. There's always been guidance, but you had to seek it out. I believe now they seek you out as well. That's a question better asked to a first or second year, sorry.
Research is incredibly easy to do. Since Sinai is a top 15-20 institution for NIH funding and since there are no undergrads competing to do research, all of the opportunities go to you. Most students do some form of research and a large portion do (funded) research between the first and second summers. A lot of students carry these projects on throughout the year. I had various projects that I was a part of all years at Sinai, including third year, although obviously not full time as it was during the summer. Sinai does push its students to do research, but you are in no way obligated to do so if you hate research. I would encourage it, though, because it really helps for your residency application.
Social life is very active and there is plenty of time to take advantage of NYC during the first two years. There are lots of bars on 2nd and 3rd ave in the lower 90s. The closest bar is just across the street from Aron Hall (called Hanrattys) so if you don't want to travel far you can grab a drink there. Many students travel to the downtown/LES/village/westside for dinner or drinks, and since Sinai is close to the 6 and crosstown bus, it's easy to get anywhere in the city. There are many parties at bars and clubs, especially during the first year, so if that's your thing you will enjoy it. Sinai's location is good, but not great. The restaurants and bars in the immediate vicinity (2-3 block radius) is a bit lacking and sometimes you have to walk a little further. NYU is in a better area in terms of this.