This is a collection of things I have found enormously useful - a mixture of websites, documents and YouTube videos etc.
Harry's Astro Shed - Pixinsight tutorials - invaluable for getting your head around Pixinsight!
AstroTortilla - making sense of this complex but powerful programme
Hubble palette - how to create Hubble palette images from narrowband data with Photoshop
Calculating a scopes focal length - very accurately.
Deconvolution in Pixinsight by Richard Bloch
Calibration and Stacking in Pixinsight by Richard Bloch