Mike,
Here is what I would recommend. First and foremost make sure that your nComputing and your thin clients are RDC compatible and all your apps, e.g. Medisoft PM are RDS compatible.
I would set up your nComputing and connect your thin clients to the domain. Set up SBS 2011 Essentials as your host computer with domain controller, which has all of the FSMO roles. As stated, no other SBS computer can be on the same domain and why would you want to anyway? Use Windows Server 2008 as your RDS server which should have all apps you want to use and all should be connected to the host server if the app, like AC, has a database. All of the apps should be installed on the host server, SBS 2011, as well. You can locate the FSMO roles with netdom query FSMO at an elevated command prompt.
You need to install the terminal server role with the correct licensing on the RDS. A licese server will need to be installed preferably on SBS.
As you stated, your thin clients will access AC and Medisoft and whatever else from the RDS.
If you add a fax server, this can be added to either server. Just make sure it is a Mainpine Fax Board. Not to repeat myself, but make sure it is a Mainepine Fax Board. Obviously, everything should be 64-bit.
One good habit to get into is calling it RDSS. Remote Desktop Services Server. Forget TS ever existed. It is RDS in the office and RDS remotely.
Yes, server 2 (Server 2008) can access server 1 (SBS). This is how the app you RDC to gets its data. No, you cannot remote to the thin clients directly. But, you can remote to RDS or SBS. However multiple users cannot connect to SBS. There should not be much of a delay between the servers. Nor the thin clients once connected.
Another user who doesn't want SharePoint, the greatest app Bill Gates ever made.
