I am wondering the same thing. What did you end up doing?
There are many existing discussions about part numbering (also look on EngTips.com) - if your system is not set you may want to research that more. One thought is you have 3 extra characters on the front that users have to type every time (eg AA-), is it worth it to distinguish between parts and assemblies this way? Having one system for both file types would reduce your complexity.
When you say "Dwg Drawings" do you mean AutoCAD format, or was that a generic use of the term - and you meant .slddrw? ...With AutoCAD you wouldn't be able to sort by file type to distinguish between part and assembly. I assume the "Parts" and "Sub Assemblies" folders are for stuff that is reused across projects.
We actually put the Part Number and a short description in our file names (eg 33140 - Bracket, Fan.sldprt), and I like that system - with or without PDM.
We generally don't have different folders for parts and assemblies. But that could work too. We break things up by sub assembly - so a specific drill sub assy folder has that .sldasm file and all the parts in that sub assy.
It may help to talk to your users, and see what they are used to and what they would like. If you have a consistent and well thought out system then most likely they will get used to it, but it takes time.