What part of the Pacific NW? I'm in Bothell, WA.
Your questions are insightfull. I'll have to be thinking about these issues myself.
One thing different from your questions you might consider is the choice of fuel. You mentioned NG or propane. In addition to NG uncertain capacity and pressure as mentioned, I've been told NG tends to not have consistent BTU content. This seems to be quite variable, regardless of what the gas company says.
Also, King County for example will not use NG for a couple of reasons. One being the BTU content, but another is its availability following an earthquake. The NG supply or service line could be broken during an earthquake leaving a generator fueless, right when it's needed. King County uses diesel.
