What are the rules for drawing a system diagram in patent drawings?

I’ve made drawings to my patent application, presenting exemplary embodiment of a distributed network of nodes. I have few questions:

1. Must the system diagrams, illustrating nodes in distributed network, be presented as hollow, rectangular shapes? I made them as hollow, elliptic shapes, is it important?
2. I didn’t include any words or letters in those elliptic shapes, like "Node 1", "Node Alice" or whatever. I left them completely hollow, because I feel that if everything is described in drawing’s description, and the shapes themselves are referenced by numbers, there is no need to put anything in those shapes (they are clearly described as to what they are in the description itself). But I saw in other patent drawings that shapes are "named", even in presence of reference numbers. Why is that? Is it necessary?
3. In my drawings I always use an exemplary embodiment. For example, I’m presenting a network composed of 3 nodes only. And I use commonly used exemplary names for those nodes, like "Alice", "Bob", "Carol". Is using names like those clearly "only exemplary" and won’t cause problems (like someone saying that claimed invention uses precisely nodes named "Alice" or "Bob", so to design around you will only need to change the names of node)? It might seem a stupid question, but I’m really not sure.