I'm departing from the West Coast (SEA/YVR then SFO or LAX) and want to book an awards trip to JNB and then on to MRU. Is it allowable to book awards via the Pacific (SIN or BKK) in C or F class without being forced to use extra miles?

If yes, can I then book the return via Europe and the Atlantic, or once I go one direction do I need to return the same way?

Finally-- if United will balk at this entirely-- can I do it with ANA or AC miles?

Thanks in advance for any help and advice anyone can offer.