Oooh...I get it! There's a phase of wardrobe building and experimenting after joining YLF. (Many of us join after life changes of one kind or another.) And then there is the paring back phase. Totally normal!
Angie has a lot of posts on wardrobe I'd start here, defining your own essentials. And here: figuring out what to keep. And here, if you feel your wardrobe is too large.
One important idea: make a list of your various roles (e.g. teacher, partner. parent, etc.) and figure out how much time you spend, more or less, in each. You will need clothes appropriate to each role, and even if it seems extravagant at first glance, identifying the roles you have to dress for and ensuring you have at least one outfit for your main climate conditions for each role will simplify your life unbelievably and make you so much more confident. This is relevant to what you quote here: "a successful wardrobe is when no matter where you are, you still feel comfortable physically in your clothes and in your style/self-expression."
In my own case, listing my key roles allowed me to recognize that there was a reason events like X always made me nervous and unhappy. I hadn't been willing to buy clothing if X events only came up a couple of times a year. It felt wasteful. Realizing that I still needed to dress for those events helped me learn how to devise suitable outfits in advance, whether that meant buying a whole outfit or buying completer pieces that would work with other, more frequently worn separates in my closet.
To your question: how do you know if things will go together?
I don't, always...but I stick to a fairly limited colour palette, which helps, and I consider silhouette when I buy. Those are the two main determinants of whether things will actually (IRL) "go" together. Apart from that, it's kind of up to you -- you can juxtapose different levels of dressiness, different style eras, etc. So pick your key neutrals and your best colours, and eliminate (for now, at least) whatever does not fit with those parameters. Decide on a couple of silhouettes that appeal to you, and consider whether your purchases are consistent with those.
More analytical types count wears and consider cost-per-wear. It can be hugely instructive to do this! I'm in the process of keeping track right now, having not kept track for. years. I feel my lifestyle has changed and I need to get some new data! It will help me decide what needs to leave my holding zone and what can stay.
Some people make it a goal to wear each item in their wardrobe at least 30 times before donating or getting rid of it. For me, the "30 wears" guideline doesn't work except on the basis of averages -- I wear some items (my workhorse items) FAR more than 30 times before donating...and others far less. But it more or less averages out, over time.
Keep in mind that people often vastly overestimate the number of wears an item gets in a year. Of course, most of us also keep most of our clothing for more than a year. Jenn and Jenni (among others) have made careful calculations about this. For those with small to moderate sized wardrobes, most items last between 3-5 years. They either wear out, or wear out their interest by that point. For those with larger wardrobes and a fairly classic style, many wardrobe items can and do last much longer. Most of my own wardrobe is older than 5 years...but I'm feeling like I'm in a bit of a style rut, and that is partly why.
Uniform dressers are usually fine with creating a capsule of essentials and adding a few statements. Eclectic dressers get bored with that and want more statement items.
Phew. That's long winded. Sorry!
