That depends on the size of your photos and videos actually. The Mini 2 has a storage capacity of 32GB, minus a couple gigabytes for the operating system and player app. The size of graphics and videos can vary widely but as a rough estimate, if we assume an average image size of 2MB you could fit about 700 images on the Mini. If we figure an average size of 100MB for your videos, you could fit about 280 videos on there.
Of course, the Mini only caches one playlist at a time (and you have endless storage in the XOGO Manager library) so even if you have loads of graphics it's pretty unlikely that you will run out of space! Thanks again for using XOGO and feel free to reach out anytime with questions.