There's no restrictions, but I do have preferences. I would like them to be bookshelves for the mains, and wall-mounted for the surrounds. If I do 7.1, I will have the "sides" probably in the ceiling, and the rears in the back wall? Will having the side surrounds in the ceiling be absolutely terrible for sound?
Having a preferance is a good place to start. A word of advice sir. I would avoid in wall in celeing.
It does not maximize the potential... Maybe for that new 11 channel yamaha to have the ambient noise come from the sky would be real choice.. but I just dont see the reflections and the sound waves working properly being directed from the ceiling I'm straying from the point.... also in wall.. well... cabinets are made the way they are for a reason... If there are brands that make in wall cabinets with the same build quality.. cool, but you won't have a port that is tuned so you will miss something....
I would start 5.1, you may be suprised how satisfied you are! I'm over joyed with what I have, I could use 7.1, as I nearly exclusively watch big epic movies and almost all are in 7.1.
One more note.... If you can tell us what you would like to hear in a speaker and a referance point. i.e. "the b&w 803's were ok, but i want more in the mid range and a wider soundstage also they looked goofy I like a more standard look and want such and such a wood grain... etc etc." Then we can surely help you in the right direction.
the other thing you need to do is audition. then audition some more. then when you feel you decided listen to some more... and then a few more. You can't sample enough. It's only anxiousness that will force you to buy. I recomend to check out specialty shops in your area also.... big stores like BB and CC will have some ok stuff, heck you may fall in love, but also go to the small localy owned shops... those folks will be ready to impress.