Errands is tricky. If you are doing it on paper the categories need to be mutually exclusive, and if you use software you usually only have the "pick this" type of filter - no possibility to exclude certain tags, which would have opened up entirely new avenues for creative and precise tagging/filtering.
I think your "themes" approach sounds very good. I cannot remember if I have tried that, but it certainly sounds solid. Another approach that I have tried is to separate those errands that I can choose to do unprepared while already out (e.g. buy milk) from those errands that require that I take something with me (e.g. take clothes to dry cleaning). That works well, too, and should work really well on paper, but typically requires clunky double-tagging if you do it with average software. (Convenient tagging/filtering features is one of those things that remain at a surprisingly stone-age level.)
As for your subdivision of reading material, it sounds very smart, but for some reason I do not have a problem with this (don't know why; I think I read stuff, so I guess I should be having that problem.)
But I can tell you about a similar trick that I use on my normal lists (Next, Someday/Maybe etc) that you might like, because it is in a similar vein. What I do is I subdivide the tasks into Often, Normal and Seldom, depending on how often I want to review/reconsider them. My specific interpretation for the Next list items is: Often = multiple times daily; Normal = once per day; Seldom = once per week. For Someday/Maybe it is: Often = multiple times weekly; Normal = once per week; Seldom = once per quarter.