MS1 is too early to be worrying about Step prep, unless you go to a school that has a condensed pre-clinical curriculum, and the best advice is going to come from people in the classes above you at your school.
FWIW, I graduated in 2018 (so took Step I in 2016 well before it was p/f) and went to a school that had in-house exams and did biochem, physiology, and anatomy MS1 and pathology, micro, and pharm MS2. The exams and material solely covered in lectures alone would not adequately prepare you for boards. I started board prep at the beginning of MS2 but didn’t get a solid system down until the latter half of the year. What worked for me was focusing on board prep materials (i.e., pathoma, Sketchy for micro, Kaplan for pharm - as an aside I think Sketchy pharm is garbage and used old Kaplan videos for pharm that are WAY out of date now and Idk of the quality of the newer ones or any other newer resources) and then supplementing with school lecture material by annotating material/factoids covered in lectures into my Step prep materials - that way, I had material condensed into one source per subject that I could focus on that simultaneously covered board prep and material germane only to in-house exams.
As far as in-house exams, they will have no relevance to Step II as you will have NBME Shelf exams for each rotation so can just focus on board prep material for studying. I’m aware that some school do use in-house exams during clinical years, but these are by and far the exception, tend to be limited to 1-2 rotations, and/or are used in conjunction with Shelf exams.