Hi,
I am not aware of any General Purpose Guide, because it depends very much on usage scenario.
For what RDP is concerned, there are several publications around; one that analyzes diffent usage scenarios and bandwidth requirements is RDP Performance from MS (_WhitePaper.docx
as it is clear from guide, it depends on bit depth, resolution, usage, ....
If you add the multimedia extensions and USB mappings from RDP extensions, it again depends: the more your users will use these features, the more bandwidth you will need. If the browse to youtube.com and watch a video, ......multimedia redirection will use bandwidth....; if they connect a scanner and scan a document, .....bandwidth; if they print, bandwidth, ....
Another thing you have to consider is not only bandwith (and if it is symmetric, such as HDSL/Fibre or asymmetric such ADSL) but latency as well: the higher latency, the worse experience for user (unresponsive feeling).
You have to test the solution quite well in the different scenarios, because most VDI solution are always demonstrated in LAN environments, but when you go an a WAN it is a completely different story.....
What I can suggest is that you pick a panel of 10 representative users, set them up using the demo licenses and monitor a normal work activity for a couple of weeks,...