1. Can the latest license work with older controllers, or do we need more licenses to communicate with controllers programmed with Step 7 5.4 (or older)?
--> Step7 5.5 license will work with Step7 5.4 this I have checked and it works. We can generalize that licences are downward compatible.
2. Can we download the programs in the controller with this software, or is it strictly what you see is what you get without the original project files (meaning the tags are not part of the downloaded project)? What about comments? I assume those are only in the project files and not loaded into the controller.
--> Tag names, and comments are in orignal file and is not loaded into controller.
3. What would most experienced equipment builders suggest? I have worked on both sides of this one and think it is better to have at least read-only access to the PLC as a customer. As an equipment builder, the less my customer would be able to mess up, the more likely it will work for a very long time :)
--> We send controller which are read/write protected. It depends actually.