I am pretty sure that I could argue against darn near every point that the OP offers. And, for what it is worth, I used to feel much the same way when I was new to the hobby of finding, restoring and riding vintage bicycles.
In my experience,
not what I have read from others, but what I have actually experienced, there are no rules of thumb for finding, restoring and riding vintage bicycles (I speak only of vintage road bicycles and some roadsters). Components do little to define a quality bike. A good component can easily be installed on a non-quality bike and visa versa. A top of the line frame and fork set might not be all that great for casual riding. The list of arguments can expand from here.
I'M NOT AN EXPERT! I'M ASKING FOR FEEDBACK ON RULES OF THUMB COLLECTED FROM EXPERTS.
What experts? You don't honestly think that we are all experts? I know for one thing for sure, when it comes to vintage road bicycles - I AM NOT AN EXPERT. Are there any experts here at the Bike Forums? Might be a couple but most are just back yard mechanics, just like me and, perhaps, the OP.