Backing up photos/videos, am I doing it right?

[cassiopeia]

My 256Gb iPad Pro is almost full so I want to transfer all of the photos/videos from my Ipad to my PC, which is taking about 156Gb of space, and then delete all photos/videos from my Ipad. The way I'm doing it is by connecting the iPad to my PC with a USB C cable and copy/pasting the entire DCIM folder to my Windows desktop using Windows Explorer. Once this is done, can I safely delete all these files from my Ipad? If so, should I delete them by selecting them in the PhotoAlbum App/delete or can I use Windows Explorer to delete all DCIM subfolders? Thanks
On a separate note, Windows Explorer is showing that it'll take about 4.5 hours for the DCIM folder to transfer....any way to speed this up? Or is this normal?