I've attempted to reply to this thread at least 3 or 4 times & each time delete what I've written, because I can't seem to express my thoughts coherently yet! But I loved reading it (and the marvelous comments), and it provided lots of food for thought, so I'm going to share my response anyway in case it's of any benefit to you.
As far as I understand it, you're aiming for simplicity as in 'less 'stuff'' in both your closet and outfits (stuff being colours, layers, etc.) but not minimalism as in tiny wardrobe or only neutral classics. For me personally, simplicity has better connotations than minimalism; I associate it with voluntary simplicity and a kind of William Morris attitude to life whereas the minimalism movement (in my brain only) almost seeks to disconnect emotions from objects, rendering it 'just stuff.' I aspire to the former but not the latter, and aside from my closet and bookshelves I do a pretty good job of 'just enough.' You strike me as already possessing a quite tightly edited colour palette and silhouette choices: which colours/silhouettes would you eliminate?
From a style perspective, minimalist style in my mind's eye conjures up a lot of black, white, and grey, structural/avant garde outfits. Lots of straight lines and sleek pieces, but not necessarily against layering/multiple pieces. I can't see minimalist style fitting in at a 50s themed party, say. Unless it opted for Buddy Holly glasses and a strict black suit with white shirt. Maybe. Whereas simplicity conjures up images of what the Amish and Victorian governesses might wear, if they suddenly found themselves in our culture. Still an emphasis on neutrals and nice, hard wearing materials, but somehow more of a timeless than futuristic feel and definitely fewer items of clothing at one time. Quieter, but a self-possessed kind of quiet. Simplicity is about letting the clothes fade a bit so that you shine more, while minimalist clothes make a statement and are more visible. Sometimes I enjoy dressing simply, but I can't imagine myself in minimalist styles (again, this is just my gut feel, so I hope I'm not offending anyone! I deeply admire people who dress in minimalist styles, it's just not for me).
I don't think I'd describe my everyday style as simple, and yet I do have a limited colour palette and a couple of uniforms I stick with. So my getting dressed process is fairly simple: do I want to wear a skirt or trousers (or a dress, which is a skirt subtype I suppose in my 'system')? Woven blouse or knit? Colour or neutral or a combination? Layer or not? And my answers to one or two of those questions automatically solves the others, so I very rarely struggle. I could probably make a flowchart of my outfit decisions, and it wouldn't be a very complicated on either! But I have so much variety within each category, and I love mixing things (colour/texture/etc.) so much, I never get bored. I often think I should probably cut my wardrobe down, but then it grew to the size it did because I kept wishing I had item X in colour/fabric/cut Y. So I've decided as long as I have the space, and don't feel overwhelmed in the morning/on laundry day/etc. to not worry so much about the numbers.