Very nice itinerary, should be a great trip. The only suggestion I'd make on it, especially if you end up making other changes that trigger the $125 fee is your SYD-xxx-BOM.

Personally I'd much rather do it on CX than MH, but CX is a morning departure from SYD and MH is a late evening departure. The CX experience is quite a bit better though, both flights are in their long haul configuration (A359 and 77W on the dates I referenced) while MH is an A330 (generally fine) to KUL but a 737 to BOM.

The CX F lounge is quite a bit nicer than the MH Platinum Lounge. Both have restaurant style dining from a menu and actually MH does have a pretty good menu in there. My biggest gripe about the MH lounge is they have no liquor in the lounge, the bar is in the business lounge and you have to request what you want from the lounge staff each time. I did notice them getting more proactive after a while and asking if I need a refill, but I prefer either self service or a bartender right there. The MH Platinum lounge is also significantly smaller than CX's F lounge, and CX has the complementary massage in the spa. MH is also a pain if you have to transfer between the satellite terminal (all long haul flights) and the regional one (main building) since their train has been broken for quite some time and no definite timeline in getting it fixed, so currently they are running busses between the terminals.

MH is certainly not a 'bad' experience but it's not nearly as good as CX.