If you have an 8841 you can just use that to develop against. Cisco IP Communicator is end of life and is a different beast to work with if you are targeting the 8800 series.
I'm rather new at this myself but I've used Ruby/Rack to deliver an application, and PHP in the past - the biggest challenge for me was making sure to set the content type correctly. If you're going to use a serializer or something to dispense the XML and it doesn't do exactly what you want it will be a it obnoxious but not impossible.
The document you're referencing is probably the best reference I've used, aside from searching for others who have stepped in bizarre bugs or issues. Just about anything I've thrown at the 8800 seems to work if it's close enough to spec. I feel like in these instead of the 7900s they are using some generic browser item with a parser that attempts to emulate earlier devices, so you can get away with a bit more as long as it makes it there.