Will I need to send my first-semester transcripts/final grades to the collages I have been accepted to?
Yes, and your final grades as well. This would apply whether you are a high school senior or a transfer student.
Will the college notify when they are due?
In general, the applicant is responsible for knowing the due dates. Most colleges list key dates on their websites. Additionally, it is unlikely that you are the first person from your HS to apply to college; your GC knows the drill. mid-year transcripts are sent when finalized in Jan/Feb, and year-end are sent when they are finalized in June/July.