Iselin is very pretty and slightly unusual. At first, I wanted to pronounce it similarly to insulin then I considered the pronunciation Eye-sul-in, and lastly I looked it up and saw is-e-LEEN.
As for nick names, most people are pretty considerate about using the name you introduce yourself with where I live and wouldn't automatically alter your name without permission, but I live in the United States. If Australians tend to call people by nick names unless distinctly told not to, then the nick name Izzy might be a concern. However, if you aren't going to stay in Australia long term and are planning to move back to Norway then it might not be a big deal if Australians like to thrust nick names onto people or not. Isel or Lin might be alternative nick names.
Iselin Judith
Iselin Athena
Iselin Bianca
Iselin Beatrice
Iselin Regina
Iselin Aisling
Iselin Yseult
Iselin Ruth
Iselin Liora
Iselin Aurora
Iselin Demetria
Iselin Frances