Curiosa - I think your plans are excellent but I don't know if they'll come off! Although dh and I are both English, and so you'd expect us to only use English at home, in fact we end up speaking Bulgarian to Poppy too (with our terrible accents and grammatical mistakes...
)
In reality, you tend to start speaking the language that your child has - which in the early years is a total mish-mash of stuff. If you are really strict I guess you can keep the language distinct, but for us, being able to
communicate with our daughter has been so much more important than sticking only to English. She has been slow to pick up English (normal, for bilinguals they say), and she has certain things which she only says in Bulgarian. Since she doesn't react when we say those things in English, we tend to say them in Bulgarian, and use the mish-mash that she uses. That's how creole languages get created! E.g. Poppy doesn't understand "do you want", but she knows it in Bulgarian, so we ask her "iskash li juice?"
Before having Poppy I would have agreed with you that it's better to stick to one language, but in reality just getting the message across and relieving the frustration tends to win the day. I wholeheartedly believe that it doesn't matter and that her brain is sorting it all out, and eventually she will be totally bilingual. But then we are in a slightly different situation to you.
Fluxuspoem - I think your plan is theoretically good too, but what language will you use when you have a 3-way conversation?