If you want to use avios on oneway tickets oneworld partners, you can transfer them to BA to redeem. Indeed, I would recommend BA Avios bookings in general for anything not directly IB or IB partners.
As far as the strategy, it is the second option. You pay by each segment.
Read this thread in the BA forum for the general idea.
http://www.flyertalk.com/forum/briti...os-2014-a.html