Thanks so much for reading!
For prints, I would bring no more than 5 copies of each design. It would seem like a really low number, but trust me, any more than that and it'll seem like way too much inventory! The first time I made prints I had about 7 to 10 copies of each, and it was about 15 designs or so. Turned out to be freakishly expensive and I probably sold about 3 of each anyway. If you do 5, it'll be enough to gauge how well a design sells. And since you'll have lots of different designs, it will mean more options for your customers!
I hope this helped ^^ Best of luck to you on your first artist alley!