1. I'm not sure there is, but it's certainly not less than 500GB.
2. Why do you want to partition? It's not necessary to partition an external drive, just use different folders.
Surface Pro (2017) vs Surface Pro 4
Where HTML5 is headed next
MacBook Pro v Surface Pro 5
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.