1. Slide 3 shows a pool of resources, which must have a size associated with them to indicate how many individual resources of the specified type are actually available. In this particular case, there's only 1, which is the default.
Slide 7 shows a pool of data flow objects, in this case, of the data_str stream type. Data flow object pools do not have an explicit size, since the scenario itself defines how many objects of the given type are required. In effect, each action that produces an output of the desired flow object type creates a new instance in the pool that can be bound (explicitly or implicitly) to a corresponding action input. Note that for state flow objects, there is always only one instance of the object in the pool.
Session 4 of this course is coming soon and will explain these details more thoroughly.
2. Naming the locked resource allows the action to place constraints on the resource. The names are local to the action, so read_in_a::u_busy and write_out_a::u_busy are distinct.
3. int[4..1024] indicates the valid values for size.
Hope this helps. Thanks for the feedback.