drewmeister_sd :

Probably a lot has been answered for you already, but ....

SA do not operate HKG/KUL. In any event, we do not have a ZED with SA.
For that matter, we do not have one with MH or CX.
Both carriers are ID90.

The fare for CX is $96 return + $30.17 taxes return.
One way $57 + $15.41 taxes.

The fares are common rated for MH.

You could, if you wanted to, fly HKG/SIN on UA and enjoy the front 2 cabins.
SIN/KUL - I have taken the bus. It was fun, comfortable and travelled through the night.
Or you can fly, it's a shorter sector, cheaper and frequencies are great.

SIN/KUL you need to forget SQ, it's ID75.
On MH, the one way fare is : $ 10.00 + $ 14.75

These rates are subject to change since I have calculated based on local currency converted to USD today.

For loads, I tend to visit the website of the carrier in question, attempt to book the maximum number of seats it allows you on their booking engine.
This of course does not allow for their own overbooking profile, but it lends some indication.

The preference is contact someone you know at the airline directly, their reservations office or this forum.

If you need specific assistance regarding UA/Interline travel, send me a private message via the forum and I'll try and help
you that way.