I'm planning a summer holiday to Austrialia for the family next year and we'd like to fly in J-class. We live in the UK.

Running the numbers for four of us, it looks to be about £9k cheaper if we fly from Oslo via LHR & SIN Sydney than a straight LHR>SIN.SYD despite it being the literal same planes we'd end up on anyway.
Couple of questions:

1. I understand the (lack of) logic to flight costs, but I assume there's no way around the fact I'll need to fly to/back from Oslo to benefit from this fare?

2. Is there any issue purchasing the flight in Norweigian currency which is what the Singapore website seems to default to (assume set from the first country you fly from).
I don't really care, but want to make sure they won't mind that we're not Norweigian residents

Then the only choice is do I pick the 380 or 777 as both legs appear to run both planes at various times.

Thanks