There were a lot of great classes I had the pleasure of taking these past two semesters! As I am an environmental science major, I had to take bsci160 and 161 and I ended up really enjoying them. Especially the lab, bsci161, as we got to participate in an actual experiment where we went out and compared the diversity of woody plants in edge habitat versus interior habitat. To choose classes you will enjoy, make sure to look into the curriculum of the class before you take it, it's very helpful for seeing how much workload you will have. I also took Spanish these past two semesters. If you were taking a language in high school and you still have interest, definitely take the FLPT (foreign language placement test) to get into the right class for your proficiency level. My first class of college ever was my 200 level spanish class, I was really intimidated to be in a higher level class like that (there weren't many freshman) but everyone was very nice.
Another class that stood out to me was HIST289A, which was an I-series class about the history of Medieval Spain and how the three most common religions there (Islam, Judaism, Christianity) interacted with each other in that region. I-series classes are limited time classes that are on an exceptional topic, and I thought this was a fascinating class because in general I like history, and it tied the subject matter into present-day reasons for political tensions. Also, there were people of all religious backgrounds in that class and it was fascinating to hear from my classmates about how their own experiences related to the material. Do not be intimidated by highly academic, dense material, as the discussion and lecture for this class helped me to understand it more deeply.
My advice to those who want to develop a mentoring relationship with faculty is to interact with them! Professors like people who are involved and participating, and kindness gets you a long way. In addition, seek out opportunities, don't necessarily wait for them to come to you. There are a lot of opportunities for TAing, and getting internships and such like that. Also, have confidence when you are applying to things, the worst that can happen is that you don't get what you are applying for.
On the topic of adjusting to university life, I am lucky in that a few of my friends from highschool go to UMD, so I am still in touch with them. However, for making new friends, I would say joining clubs and group chats to do with the program you are in (for example, there is a Scholars program discord) is your best bet. Also, there are often groupme chats for your classes so I would recommend joining those so you can stay in contact with people in your class! Hopefully, you will have a lot more opportunity than I to be able to organically become friends with people, as online you can't walk to classes with people or have side conversations much. I also think that forming a study group for your classes is an effective way to study and build relationships with people at the same time. Anyways, there were certain aspects of university academic life I was not prepared for! For example, the workload that comes with 19 credits and TAing a class in the second semester. Make sure not to bite off more than you can chew, I got through this semester but it was tough. I would recommend that you take a lighter load of credits in your freshman year if possible.