An inventory is the foundation for every other wardrobe calculation. Cost per wear needs the price and the wear count; spotting duplicates needs the list; identifying what you never wear needs the record.
Six columns are enough: item, category, colour, purchase date, price and times worn.
The common mistake is trying to catalogue everything at once, and abandoning it halfway. Start with one category, and count wears forward from today rather than trying to reconstruct the past.