I ended up booking the LH A380 and SA A346 on the way home. I just have a question regarding earning miles.

100% status miles are earned on the following (econ) classes:

AC: M, U, H, Q, V, W, S, K, L, T
LH: Y, B, M, H, Q, V, G, U
SA: Y, B, M, K, H, S, Q

If a travel agent books the flights go for me, are they allowed to book one fare class for one segement, and another for the rest?

Ie. If my route was:
YVR (AC) --> FRA
FRA (LH) --> JNB

could the AC leg be B (so I could instant upgrade) and the LH be U?

How do you pick which fare class you want to ensure you get miles? If my route was:

JNB --> FRA (LH ticket, operated by SA)
FRA --> YVR (AC ticket)

Assuming each letter gets mapped to itself in the other carrier, the lowest fare class between the LH and SA fare classes that would earn 100% status miles is Q. Is that correct?

Thanks