I share John’s concern that something may be amiss with your references that support the statement, "At 0F, you 1/2 the average persons base metabolism is used warming air." This value should be in the 10 - 12.5% range rather than 50%.
The sleeping bag system provides resistance to the heat exchange between the human body and environment. Heat is lost from the warm body to the cold environment by dry heat transfer (conduction, convection, radiation) and by evaporation of sweat from the skin surface. Heat is also lost through respiration (convective and evaporative losses). When a person is sedentary and comfortable, approximately 25% of his/her heat is lost via respiration and perspiration at the skin surface. The remaining 75% is from dry heat loss from the body surface (ASHRAE, 1997); this is the heat loss that sleeping bag systems are designed to minimize. In addition to ASHRAE model all other models I am familiar with use an average 10 - 12.5% for respiration.
I just looked up the Artic respiration heat loss value in the, “United States Naval Flight Surgeon's Manual: Third Edition 1991: Chapter 20: Thermal Stresses and Injuries”. It states, “Vaporization of water removes heat from the skin surface and the moist mucous membranes of the respiratory epithelium. When one gram of water is converted into water vapor, 0.58 kilocalories of heat must be supplied from the surroundings for the conversion to occur. Although the actual amount of heat loss depends on the ambient relative humidity, in Antarctica, where humidity is very low, respiration alone may account for ten percent (375 kcal) of an individual's total daily heat loss. Insensible perspiration, as is shown in a later section, accounts for an additional loss of about 400 kcal.” Note the 10% value for Artic respiration.
70 Kcal/hour is effectively the same as the 70.77 Kcal/hour BMR value used in the ISO 8996 (2004) International standard. Most physiology models list the constituent components of heat loss as 12.5% (= 8.8 Kcal/hour) respiration, 12.5% (= 8.8 Kcal/hour) insensible perspiration, and 75% dry heat loss (= 53.1 Kcal/hour). I assume that they made a mistake listing 18 Kcal/hr as convection rather than evaporation and things just got more confused after that.
The relevant text on page 23 says, "In Hypothermia, Death by Exposure, Dr. William Forgey notes that at 0 F, and average man's convective heat loss due to warming of incoming air is approximately 18 calories per hour." The warming of incoming air is not a convection loss, it is an evaporation loss.
Other than this respiration loss point of contention, I believe all of your other staying-warm-suggestions, and those from the other posters, is excellent advice.