First off, you are building a great collection. (Waving at my Sweetie twin!)
I also wear booties for about half the year, seriously. And my wardrobe is cool toned. And here is what I have discovered works really well for me.
1. One BASIC bootie. Mine's an almond toe (almost pointed) Stuart Weitzman chelsea boot. Oh, I love the simple lines of these, and they are black. Simple, but works with almost anything.
2. One coloured bootie. For me, this is the Munro Robyn, in a cranberry colour. It works well with skirts as well as with pants because of the V shaped vamp.
3. One animal print bootie. At the moment, I have the SE Pettys in a python print that harmonizes well with grey, black, taupe, white, cream, and navy, or of course denim.
4. One "bookending" bootie. For me, that is taupe. I have an older pair of Reports -- they are not ideal and I need to upgrade to a sleeker bootie as soon as I can find it.
5. One "wild card" bootie. I got a pair of ink blue neoprene topped Zara pointy toed booties last year that were my most worn item.
I also own a "dressy" bootie (more like a shootie) in bronze, with a narrower heel.
And I would LOVE to add a leopard print one. I would wear the heck out of that.
So -- this is my system. I think once you have "basic" or "core" and "bookending" covered, you can go crazy!
But note -- "bookending" isn't always literal. My blonde hair "bookends" with taupe, grey, leopard, phython. And cream (if I could find it). It would even harmonize all right with cognac.
So just because your hair is dark brown doesn't mean you have to have dark brown boots. In your case, any dark boot is going to go the job.