N/S elongates the finger and suited to a large stone. A small finger is unlikely to accommodate a large oval set E/W due to insufficient finger real estate.
It is a stunning ring!!! I would say it depends on the size of the stone. If it's an exact replica, you wouldn't need to have it set E/W since the stone would be enormous, but if you're getting a smaller stone then e/w would work and it'd look nice. Either way, it will look stunning!
your fingers arent big! And a 5ct stone would look awesome on you! Personally, I think you could leave it n/s, but if you want more finger coverage then go e/w.
Even with that finger size, I doubt you'll have the finger real estate to wear a 5 ct coloured stone set E/W. Pictured below is a 4 ct spinel measuring 10 x 8 mm on a size 4.5 finger. As you can see, it takes up almost all side to side space as it is when N/S.