Winterization clarification

I have used compressed air (60 - 75 psi) to winterize my 177 since 2012 with no ill effects or leaks.
To answer your above questions"
1) I have always set the 3 valves to "bypass."  I pull the drain plug on the HW tank and drain that way, seems like it would take a long time to drain that tank by using compressed air.  Also I have an access cut under the mattress so it takes less than 1 minute to raise the mattress, open the cover and switch the 3 valves. 
2) You are absolutely correct, you are only bypassing the HW tank.
3) By opening the drain for the fresh water tank until no more comes out you are good to go.  Sure there may be a couple quarts or so in it when no more comes out of the tank, but there is plenty of room for expansion when it freezes, so no worries. Do not put anti-freeze in your tank, not necessary plus it will give you a nasty taste if you use it for drinking water as we use our fresh water tank for drinking.
4)  Yes and Yes.  You are correct.
5)  As you clear you lines of water by compressed air, the expelled water will run into you drains and then into their respective holding tanks, so I leave mine open as well during this procedure, the amount of water is minimal, a quart of so in the gray water tank, and less than a pint in the black water from your toilet.  When finishing blowing out, simply close the gate valves and then pour your anti-freeze in your traps.  I use about 1 pint total for my 2 sink traps, 1 shower trap and just a bit on top of the toilet valve.

I am fortunate to live where I don't have to winterize typically, almost never gets below freezing.  Just my two cents though, the whole idea of winterizing is to get the water out of the small tight areas like hoses and valves to prevent damage from water freezing and expanding.  If your HWH bypass has never had water in it, you can probably get away with not blowing it out and just doing as you suggested, drain and reseal the WHW and then blow it out without using the bypass.  However if any water has gotten into the bypass line in the past and the edges of the valves you could have a problem if you don't blow them out as well. I may very well be wrong but it makes sense to me.  I happen to be tall and I can actually reach the bypass valves under my 178 bed from the access panel in the storage area in the back.  It is a stretch but doable by feel, especially if you are thin enough to actually crawl into the storage a little bit (not my case, but ape arms help). Lifting that bed is not easy and then trying to get under the panel while holding it up is not fun. The screws have never been taken out to be able to lift the panel so the previous owners either never winterized or did what I do and reached the valves from the access panel.  Good luck