Novos,
Welcome. First thing to work out is can you get a Sudan visa easily (has put off most of us here who are not quite willing to risk a denied boarding before attempting a transit without visa).
On your questons.
1/2. I think it will be an AONE5 - the Asian exception only applies to EMEA-SWP (ie basically LHR-SYD/MEL) on single plane/ transit. This should mean you can stopover in HKG.
3. unsure
4. soth america is not great for A routes. maybe do a few more in asia if you want them (CX still runs A on a limited number)
5. change in price will be limited to fuel fines and UK APD (if only transiting LHR this will save a bit). fuel fines governed by ticketing carrier. AA may be cheaper
6. no