Woah. Hold the phone. This isn't going to work from what I can tell.
The wife bought me a Soda Stream for Christmas. It comes with one very thick 1L PET bottle. It has labels all over it that say very clearly to only carbonate plain water, then add flavorings. With the model I have, you can only thread on PET bottles. I don't see a way to easily disassemble the CO2 tube mechanism in case it got gunked up, which is why they probably want you to carb the plain water alone, to prevent bacterial infections. How you'd hook it up to a glass bottle is beyond me. I know there's a glass version available in the $200 range, but I don't have much knowledge of that one.
Also, supposedly you can't refill the Soda Stream tanks. You're supposed to exchange for a charged 60L canister. At $10 for less than 1# of CO2, that's pretty steep. I wouldn't mind so much if the housing it sits in didn't feel so darn cheap.
You're already out the door $80 with the base model, $200 with the glass model. You're better off buying a 5# tank ($60), getting it filled ($10), getting a basic regulator ($50) and using one of the many CO2-tank-to-PET-bottle adapters available ($15). The same 5# canister will last many times longer and cost the same to refill. If you decide to keg later, the tank and regulator can be utilized for that too. Both take up the same amount of space.