Hi Jeff,
I prefer if you follow the same coding style. If you want to make a service on top of the business layer after the fact that's ok but I'm not a fan of making server side web requests when everything is running on the same server and the business objects can be accessed directly without that extra overhead.
I also prefer if things can still work when javascript is disabled but the experience can be enhanced by javascript but should be functional even with it disabled. Most things in ASP.NET WebForms do work even if javascript is disabled except for things like LinkButton or Autopostback on dropdown lists. So for example a feature could be built using the traditional webforms postback approach and it should be possible for it to work without javascript. But if you then want to dress it up with ajaxy javascript that calls services thats great so long as it can degrade and still be functional without it.
My advice is just work on and complete one thing to start. ie don't mess with workflow right now. If after private messaging is complete you want to do something with that we can consider it but the more wide ranging changes you propose at one time the less appealing and more distracting it is for me.
Also I won't be able to even look at your code until I receive a contributor agreement. Note that the current pdf has an incorrect old address, I will see about updating it soon but the correct address to mail it to is PO Box 1978, Concord, NC 28026
Best,
Joe