If we follow Disney's numbers, we should expect around 500 Rooms per night for whatever UEU's hotel will have, as MiraCosta, Disneyland Hotel Paris (Even though the outlier is Grand Californian).
If we had the amount of hotel rooms for the In-Park hotel of USB, that could give us a potential number to go off of as a potential guess. And to be somewhat frank..I do not think the In-Park Hotel for UEU, will be the only hotel at the property in the beginning.