Hi Raw33,
My opinion would be to take this project slow and build it up over time as your experience and knowledge increases.
Your room will probably be your biggest issue. A lot of reflective surfaces which more than likely will cause sound quality issues. It does sound like it might be a large room which should help. The good news is that sound issues with the room the can be fixed. Things like furniture, throw rugs, drapes can all help to reduce reflections. If you live near a major metropolitan area you should have someone in your area that deals with room acoustics that could come out on a consultation. It might set you back a few bucks but it would probably be money well spent.
As far as the system I would start out with a 2 channel music system just to keep it simple and your investment manageable. You can always expand in the future. The more parts you add the more complex the integration becomes and if it’s not integrated well you are not going to be happy. Find a dealer that will at least give you a return option after some type of home trial of so many days. Usually these are 30 to 45 depending probably on the dealer and the manufacturers involved. A good dealer should also be able to help you set your system up.
If you buy decent quality gear and it is properly set up and in your case the room is properly treated, it should sound good doing both music and home theater.