I’ve spent many hours (this does get addictive doesn’t it), getting my itinerary in shape and trying to optimize credits/miles on BA-EC (of which I’m not yet a member). Using ONE validator, I’m confident that my AONE5 itinerary is valid (sorry to bother you last week with questions about that), so my remaining questions mostly involve BA credits. There seem to be a number of BA experts here, but tell me if I should post this on the BA forum instead.
Here is the plan:
Prior to the RTW, I’ll purchase a separate ticket and fly economy: YVR-LHR(on BA)-CAI(on BA).
My AONE5 itinerary is:
Segments 1-3: CAI-LHR(on BA)-CPT(on BA), JNB-SYD (Thus at this stage: 4 BA flights and 660points=Silver?)
Segments: 4-14: BNE-CHC-SYD(codeshared BA)-MEL(codeshared BA)-SYD(codeshared BA)-BKK(on BA)-HKG-DPS-HKG-BOM-HKG-LAX,
Separate ticket: LAX-DFW(on AA)
Segment 15-17: DFW-YVR (Thus at this stage: 4 more BA flights assuming code shared count and 1500 points post-Silver=Gold?)-JFK-DFW.
Return part of separate ticket: DFW-LAX (on AA)
Segments 18-19: LAX-LHR(on BA)-CAI(on BA). End of AONE5.
Then using the return part of the separately purchased initial ticket: CAI-LHR(on BA)-YVR(on BA). Thus 2100 points and 4 BA segments after reaching Gold.

I have the following questions:
I assume that the code shared BA/QF segments (CHC-SYD-MEL-SYD) will count toward the required BA 4 segments to reach gold status? Otherwise it seems hard to get BA segments in SWP/Asia/NA.
Does having 4 more BA segments after Gold do anything for me in terms of extension of the Gold status?
I assume I can buy the fifth Asia segment (I had to remove one of them to run the Validator)?
Any suggestion for the unused segment?

Final comment: Over the past week, I’ve spent more than 40 hours on FT. The amount of very helpful information is amazing. I feel that I have learned a lot. (A week ago, my message above would have been incomprehensible to me).