I'm curious about the motivation for your boundaries, and whether you intend them to be permanent or just temporary until you are more comfortable with this lifestyle. If they are temporary, what are you doing to work beyond them and remove these restrictions? If they are permanent, how do you rationalize that this will work in the long term?
I especially don't understand why your husband and the other woman aren't allowed to communicate without you. That seems extremely insecure.
While I can understand why you think that only-threesome-sex makes sense in theory, I don't see it as being remotely practical. Clearly, your husband's and this woman's sex drives are higher than yours. When you're tired, they're still ready to go. You met this girl with the intention of pursuing this relationship, but they're only allowed to do anything when you're in the mood. When they are both horny and you just want to sleep, what are your honest expectations? Are they supposed to lie there and just dream about it? Go to the bathroom separately and masturbate? Pressure you into having sex when you're not in the mood?
“As I am sure any cat owner will be able to tell you,
someone else putting you in a box is entirely different
from getting into a box yourself.” —bisexualbaker