Cutting categories down to five or eight leaves an immediate itch. “So how do I show that this one is for beginners?” “I want to list only the posts written for marketers.”
The answer is not to add categories back. It is to separate the axes.
Several axes need several taxonomies
A post has more than one property. What it is about (subject), who it is for (audience), how hard it is (difficulty). These are independent of one another — there are difficult SEO articles and easy ones.
Force all three into a single category tree and you get combinations like “SEO / marketer / beginner”, and combinations multiply. Seven subjects by five audiences by three levels is 105 archives, nearly all of them shells holding a post or two.
Separating the axes turns multiplication into addition: 7 + 5 + 3, fifteen archives offering the same filtering. WordPress supports this separation natively, and you can register further taxonomies when a genuine new axis appears.
Tag freely, but with a purpose
Because tags have no limit, they are the easiest thing to let go feral. The classic failure is more tags than posts — invent a new tag per article and every tag holds exactly one thing, which groups nothing at all.
Ask one question before adding a tag: “will at least five posts eventually carry this?” If not, that phrase is a word in your copy, not a tag.
Indexing is a separate decision
Here is the part that matters. Creating a taxonomy and pushing its pages into search are two different decisions. On-site filtering is worth having; that does not mean all fifteen archives belong in a search index.
The test fits on one line: does this page carry an introduction a person wrote? A page that is nothing but a list of links gives nobody a reason to click it from search results, and a site full of them reads as thin.
Even when you keep a page out of the index, it is usual to let the links be followed: the archive itself stays out of results while crawlers still travel through it to the posts. Most SEO plugins set this per archive type in one place.
We run this site the same way — subject archives carry written introductions, while difficulty and tag archives exist purely as filters. If you would like your taxonomy and indexing policy reviewed together, it is part of the diagnostic in our optimization program, and related articles sit in the SEO archive.
Next part
With classification settled, relationships between posts come next. The following part is cannibalisation — how to find the places where two of your own pages are eating each other’s rankings.