@ccprofandmomof2 personally, I went to UCSB undergrad and UCB for grad school. I have a rising senior at UCD so can answer your questions based upon my perception of what UCD is like today.
First year STEM classes are large (not necessarily crowded but large). That said, each class has a weekly discussion with approx 30 kids as well as a lab with less than 30. The professor and TAs all have weekly office hours. There is free tutoring for math and chemistry in each dorm. As you move away from the traditional entry level chem, bio, physics and math, class sizes generally become smaller.
Classes and administration might feel impersonal and bureaucratic as a freshman but as soon as one gets the hang of it, that feeling goes away. I think that is the case at just about any school. As an example, my child got to know one of his TAs well and the TA encouraged him to try working in a lab to see if he might be interested in research. He emailed a few professors and simply said that he was a sophomore and was wondering if there were any undergrad opportunities available. He didn’t share his grades or that he knew the TA, just that he was interested. He heard back from all four professors and was offered positions in three of the labs. The fourth professor said he didn’t have space at the time but would keep his contact info if something opened up in the future. An example of things not working out was when there weren’t enough spots in the second course in a three quarter series (ex. chem) so some kids had to wait a quarter before progressing. I didn’t think that was planned well and felt that they should have been able to better estimate how many kids in Chem 1A would be taking Chem 1B.
Regarding career guidance, I think UCD is similar to the other UCs in that there is a lot available but the student needs to take the initiative to seek it out. One example at UCD is the pre-health advising with their boot camps, test prep, practice interviews, etc. https://hpa.ucdavis.edu/preparing-health-profession Another example is the MAST (Math and Science Teacher) program where they will pay for your CBEST/CSET admission test fees if you are enrolled in one of the courses. https://mast.ucdavis.edu/