Seems fine. Just can't be retrospective. You can free call Optus on +61 2 8082 5678 from any Optus mobile to order one. Or get it in the Optus app.
Note keep a strong hold on data usage. If you use your allowance then international roaming rates kick in.
Yes, you can @Couplas 🙂
If you need help adding one on, let me know & I'll help out.