There were many ways of starting a Vulcan...
Originally, back in 'Great White Deterrent' days there was the 'Mass rapid' system which used fuel/compressed air combustors to start all 4 engines simultaneously, all the PFCUs and would put all the alternators on line. This put an enormous strain on all systems and was true 'Soviet missiles inbound' stuff.
The combustor 'rapid start' system was retained in later years, but it was frequently only partially serviceable (it required compressed air bottles and trunking in the wings to be serviceable...) and was normally only required when there wasn't an external air start available (such as on the ORP). You set the throttle of the appropriate engine at 50%, then pressed the button. "Owwwoooohhh"-once it started, you brought it back to idle to shut off the rapid start fuel bleed.
The more normal technique was to use external air to start one engine at a time.
However, if all the bottles and ducting were serviceable, you could start all 4 one after another in a rippled sequence - colloquially termed a 'ripple rapid' start. Usually the captain would look after 1&2, the co-pilot 3&4... Owwwooohhh, owwwooohhh, owwooohhh, owwwooohhh - then see how many had actually started - it took mere seconds!
If there was time, but no external air, you could rapid start a single engine, then crossfeed 'engine air' bleed to start the others. There were 2 ways of doing this; either you rapid started one, then set it at 70% and started the other 3 one by one - or more dramatically set it to 93% (very noisy and hazardous!) and started the other 3 simultaneously using the 'engine airs' instead of external air. The Crew Chief was supposed to confirm that it was 'clear behind' before doing a 93% crossfeed start. My captain decided to do a 93% start at Goose Bay once when we'd been delayed - and sandblasted all the cars in the car park behind!