3. Does the ATX to A1200 adapter stick outside the back of the case and then plug into the A1200's power port?
You can certainly connect the A1200 power cable to the ATX main cable to deliver 0/5/12/-12VDC, there's plenty of information on how to do this online. You'll at least want to do it for the -12VDC line.
My tower does this and uses the floppy power port on the motherboard to boost the 0/5/12VDC lines too.
