Very important.
I do however not have to dress very femininely, jeans and a t-shirt (and generally something to cover the scars on my arms; how I wish I had not decided to repress my wish to transition as a teenager) will do, but they have to be women's jeans and t-shirts. Some of the shirts may be androgynous, but even then I at least know I picked them out by myself, because I liked them, not because I had to fit some norm. As for jeans I always wear women's slim or skinny fit models, because I like how they feel (I like that they sit in place), and because I like how they show off my hips, which were broad/feminine to begin with. Before accepting myself, I always wore loose-fitting (sometimes even baggy) suit pants because I knew I looked feminine in tight-sitting jeans.
I'm wearing more (or even very) feminine tops increasingly often these days though, and I can see myself getting rid of most of my more androgynous wardrobe in a year or so. For once in life, I see the fact that clothes from outlets like H&M wear out quickly as a good thing, as it's a good excuse to not keep them for long while transitioning.