As olster says, I don't think you need to get too much into the nitty gritty of Airbus systems.
The Airbus FBW is a fantastic machine which has been designed and developed by very clever engineers and test pilots.
Follow ECAM and the STATUS pages and do so carefully, line by line. Don't try to second guess. Don't invent your own procedures.. The Airbus people have spent a lot of time working out procedures to be correct and appropriate, while taking into account things that you or I might not know about or appreciate.
There was an Airbus Industrie publication called "A320 Family Instructor Support", dated 2001, ref: UHG1041; which was very interesting and useful, but it does not go into systems such as bleed air. It concentrated on how to fly the FBW; and the reasons for various procedures and methods, and dealing with some major failures.
I was an engineer before becoming a pilot, and I found the Airbus manuals to be clear enough, but that might be because I can follow a system or a machine from an engineering point of view.
As olster also says, I never felt the need to read other non Airbus publications about systems - these can lead you up the garden path. All you need to know is in the Airbus FCOM and FCTM, and Airbus 'Safety First'. It might well take several concentrated read throughs, to understand a system.