How many photos/videos can you have before you need to upgrade your iCloud storage?

That’s an impossible question to answer, without knowing the size of the photos, and more important, the size of each of the videos. You can estimate photos using 4 MB each, but a video can be anything from 4 MB to 500 MB or even more. Go to Settings/General/iPhone Storage and see how much space is allocated to photos. That is the minimum iCloud storage you will need to sync photos and videos to iCloud.