Architecture diagram can be found here http://aivhub.com/developer

No, the source code is not redistributable, even if you change it. The only files you may distribute are explicitly listed in the EULA http://aivhub.com/docs/AIS_EULA.pdf

Yes, we have dedicated sections for developers http://aivhub.com/developer

In many instances we often use third-party license and files to continue to provide the powerful solution and add value to our existing product features, most of the work is copyrighted by their respective owner and you must refer to our third party license terms as well before making any changes to any of the third party code. Please consult our EULA for additional information http://aivhub.com/docs/AIS_EULA.pdf