iCloud photos backup

Hello Everyone,

I'm new to iCloud Photos, I just completed the upload of the entire iPhone library (7Plus) and I noticed a difference of 5 GB between the iPhone library and the online library, as well as a 506 items difference between them.

Is there anything I should know maybe about videos size?

The upload circle in settings sais 100%.

Second question is:

If I use iCloud Photos do I still need to include Photos app in the backup? Can't I restore photos from online library?

Thanks for help!