You got the framework by Chris, who also has made a series of videos describing how he made his version of the system.
The start-up idle bellow is a parallell/alternative function to the "handgas" setting on the dashboard.
The handgas should not be used for startup if the bellows is set correct.
The bellows makes starting flexible for different temperatures, as it is setting the achieved succing vacuum when start-crancing.
If well pre-set, it is usually better than a less routined driver.
It does not replace anything; it is an extra device guaranteeing enough vacuum for correct mixing ratio at cranking.
Go through Chris' all videos about it before starting a build!
This lessens misconseptions and a lot of work...