Hi,
the short answer is yes, playmaker can do all this, and if you are not afraid of scripting a bit, you'll have the winning combination!
now, with no scripting at all, I would however recommand you to get ArrayMaker as well, which will allow you to store information in arrays and hastables for reference. Without this, you would struggle big time for inventories and similar stuff.
-- networking, yes: a photon integration is currently in beta, and it works very well
-- ai and pathfinding, yes, unity pathfinding is also available in Unity
the rest of your descriptions are I think totally feasible and really is matter of design, not feasibility.
If you don't know how to script custom actions ( cause actually, playmaker building blocks are simply actions, scripted in a very standard way, meaning everything is possible), don't hesitate to ask on this forum, we'll do our best to answer and help you out.
Bye,
Jean