Hey Reiner!
The items in portfolio gris are sorted based on their creation date, i.e. by changing the “Published on” date in the “Publish” box for a particular project (in the editor mode) you can change the order in which they appear on the page. However, if you specifically need a numeric system whereby a new meta field could be assigned to hold the information about the order of the items in a numeric format, please let me know, I will provide you with a quote.
Sincerely,
Andrii / Satori Studio