Your DONE4 will be a great opportunity to rack up a lot of points, potentially qualifying you for OW Emerald.
I just checked. The routing would give me a bit above 1,500 BA tier points.
Given how cheap and easy it is to get from HEL<->OSL, you can save a lot by starting there. And instead of OSL-lhr-LAX, you could do OSL-doh-LAX, for two nice longhauls on QR.
OMG! From Norway the DONE ticket is almost EUR 1800 cheaper.