I'm not an expert on disaster recovery, but have to think of it for $day_job on occasion. The way i think about it is something along the lines of when (not if), disaster strikes, what needs to be saved vs what can wait a while to have it recovered...plus what level of effort are the different sets of activities worth. For example, if i host my public blog website on my machine at my home, and power goes out (thus making my blog unavailable during the power outage), am i ok with this, or do i need to ensure that it can be brought back up? If i feel that it needs to be brought back up during such a scenario, how much effort (which really means time plus money) do i wish to plan for? Obviously this is a vast oversimplification...but that kind of thinking has helped me bring up topics and questions in advance in order to plan for extreme scenarios...and you know what? Sometimes the things people think they "really need to be up/available" are not that important. Other times, sure, but then you commit, plan, test, and prepare for such truly essential activities. (And, of course, other times, whether the thing that needs to be recovered is important or not, you might be compelled by laws, regulations, contracts, etc...but that's a whole separate topic.)
So, again, start at the end - when disaster strikes - and consider what you think is worth keeping/bringing back up, and then plan backwards from there to make it so.
