So...the question is: Is it just me or is this what it's like for all SMs? And..does the process eventually start to make sense with experience, or is it wildly dependent on circumstances?
So my short answer is "yes and no". Working in a volunteer environment (not just theatre, but ANY time) when people are not being paid for their work there is less committment and follow-thru. What's the repercussion?
As you move up, things get more structured. Actors are required to have conflicts approved at casting. When there is more money involved, there are more people looking at how that money is being spent. When there is more money it is easier to throw money at problems if necessary which alleviates stress. But there will always be directors who have super-secret conversations with actors or designers making changes that you don't know about. There will always be people not making their deadlines.
At the lower levels, there is more rolling up your sleeves, getting your hands dirty. As you move up professionally, there is less of this... But then there is a new set of challenges and a different kind of crazy.
Every show is different and had different needs so you are having to constantly change your system, paperwork, etc. However, with the benefit of experience, you'll begin to recognize the signs and head off problems before they become problems...
I've been working for a while at the LORT level and am pretty good at what I do... But I still have at least one moment on each show where I feel totally overwhelmed, feel like I've made horrible mistakes.
My advise would be to try to work as a PA at a professional theatre in your area... You'll learn by watching a more seasoned ASM and get a better sense of what the job is/could be to decide if this is something you want to do.