View Model architecture

   From my perspective I use  1 repository as a wrapper for 1 entity.  This is not wat Ward suggested in this post before... The Items and CurrentItem properties of he repository gives me a clean and consequent binding interface. I'm in the middle of a test-evaluation process and can not share code with you at this time. I think your discission is about 1 or more entities in one repository.
for 1 entity per repository: (my way)
 The hard way is to make 1 generic class
A more simple way is to make a baseclass and subclasses for yout entities

for more entities per repository (Ward's preferred way)
Make a class containing 1 or more observable collections, create factorymethods which you can fire from you viewmodel

Add commands to your viewmodel which you can bind to xaml (MVVMlight V3.  ->commands ) works fine for me .

I'm a newbie to .net, sl, MVVM and all the other techniques an it takes a lot of effort to make these concepts working so far. Just keep reading and looking for demo's. I realy do  recommend the MVVMlight toolkit  to you, Ideablade have some demo's how to use them in your application. It takes som time to read all this, the guy who wrote this toolkit has a great video on his site.

Best regards,
Peer