The answer to Bernd Podhradsky's question on starting No 2 engine first seems to be explained in Volumes excellent link:
http://www.eucomairlines.de/manual/l500apen.zip
Powerplant Operations
ENGINE STARTING
The engines can be started using APU air, ground air (2 hoses minimum), or crossbleed air from an operating engine(s). Normally, the No. 2 engine is started with APU bleed air, and subsequent engines are started with crossbleed air from the operating en-gine(s). Do not mix APU air with engine bleed air or ground air.
The normal start sequence is engine Nos. 2, 1, and 3; however, this may be varied at the
captain's discretion. Particular care must be exercised to avoid exhaust blast damage from No. 2 engine. In this context local airport regulations may require that No. 2 engine be started after pushback. Any change in starting sequence should be coordinated with the ground personnel prior to initiating engine start.
Optimizing Air Supply
If air supply for start is marginal, close the engine HP air shutoff valve to ensure maximum air supply to the starter.
Depending on start air source, accomplish the following:
For starts using APU air:
Start No. 2 engine first because duct air pressures are generally 1 to 2 psig higher than
when starting a wing engine from the APU.
When starting No. 2 engine, if air supply is marginal, close the crossbleed valves to
ensure maximum air supply to the starter.
Minimize APU generator load to prevent electrical demands from taking priority over
air supply. For each lOkW reduction on APU generator load, the available engine
starter torque is increased by approximately 4%.
Operate an air conditioning pack during engine start to reduce surging of the APU
load compressor. This added load fully closes the surge control * valve and all
dumping ceases. However, if the duct air pressure is reduced by more than 2 psig with
the pack on, the resulting pressure may be insufficient for a proper engine start. In this
case, the pack should be turned off and the start continued, despite the air pressure
fluctuations.
For starts using ground air or crossbleed air :
Turn off all packs.
Check crossbleed valves open.
When using ground air, start a wing engine first, because for a given duct air pressure
the wing engines may spool-up faster than No. 2 engine.