I agree with Flexible Response. My employer, who operated 18-19 L1011's in very hot conditions, always started No. 2 when using the APU. After No. 2 was running the APU bleed valve was closed (the APU bleed air could not be mixed with other air sources as it might surge) and No. 2 bleed air was then used to start 1 and 3. The reason was pressure drop due to ducting length. The APU fed into the aft fuselage ducting below the horizontal stabiliser (where the APU was installed). This was the same duct used by No. 2 engine. If using ground air a wing engine was usually started first.