To answer to the Scripting part of the question:

Marking the class as static indicates that all members of the class must be static. When executing a QAction, DataMiner will look if the method is marked as static. If it's static then no instance will be created, even if the class itself is not marked as static.

Using static classes means that this class object and its static fields are shared across all the elements running on the same DMA, in the same SLScripting process. This means that element A and element B of the same protocol driver in that case have access to the same static fields in their QAction. The application domain keeps track of static objects in the managed heap. These objects stay in there as long as the DMA is active and survives the restart of an element. When using DIS inject, the element uses a static DIS object. After the DIS inject, the element will use again the original static object.

Using classes without the static keyword means that for every element QAction class there will be an instance object created. These will then have no access to the fields of other elements of the same driver running in the same SLScripting process. The instance object will not survive an element restart and will eventually be cleaned up by the garbage collector when that walks over the managed heap. When using DIS inject, the element uses a new created instance object. After DIS inject, the element will use again a new created instance object instead of the one that was used before the DIS inject. Keep this in mind when implementing a QAction that this situation could occur.

To summarize:
-If you have no fields in the QAction class then use the static keyword, there is no need to create multiple instance objects of the QAction class. If there are 100 elements on the DMA then 100 instance objects are created when not using the static keyword. If static keyword is used then you only have one static class object in memory.
-If you have static fields in the QAction class then be aware that the static keyword means that the fields are shared across elements on the same DMA: one element could overwrite the other one, locking might be needed. The data will survive an element restart. If you're 100% sure that this will be the only element of this driver in the DMA (e.g. a manager driver) or have taken the data sharing and locking in account then you can use the static keyword. Without the static keyword this is more safe, every element will have access to only its own set of data.