Dynamics 365 FO / AX - thoughts on application development and customizations

When working with customizations in Dynamics AX I consider it best practice to have several installations for the same customer. At a minimum you should have a development environment, a development test environment, a test environment besides the production environment that the customer runs in daily business. DEV. The development environment is for hacking away, developing and doing research and experiments. DEV TEST. The development test environment is for testing the customizations (inhouse QA) before releasing it to the customer for test. The transfer of customizations between DEV and DEV TEST is done by exporting and importing .xpo-files. TEST. The TEST environment is where the customer makes acceptance test of customizations. The transfer of code to the TEST enviroment is preferably done by copying layer (.aod)-files from the DEV TEST to the TEST, allowing for release/build control. If successive deliveries must be done, this can be again be done by exporting importing code AS L...