Jose-Javier-Sanchez is included. I will answer what I can
1) The Marketplace link should replace the KD which needs an update.
2) CAwiki is an internal site that should not be in the knowledge document.
3) A field pack is an extension to the product to support custom capabilities. In time, some of these could be added to the product, depending on popularity and other factors
4) Writing field packs may be covered in the APM developer Community. The github link can be found in 12 Days of CA APM - Day 11 : APM Developer Community
Please let me know if this was helpful