Love the cardigan on you. The soft muted green is beautiful -- agave, yes, but also a soft sage, or oceanside green, perhaps. Lovely! I like the pants, too, and the loafers (crossing fingers they work). Very nice combo.
Re the wrinkles on the pants -- this happens on me sometimes because
my hamstrings/ thighs need more room than a slim or straight leg or boot leg pant allows. Sizing up doesn't work for the reason you say. The pant design is relatively slim and my leg is...my leg!
It does not happen with wide leg trousers, only with slim or skinny or straight trousers or -- especially -- jeans. Happens to almost everyone with slim jeans that have stretch, in fact!
Sometimes I can fix this by keeping the length of the pant on the shorter side. This is the case when some of the problem is due simply to too much fabric, because of my shorter height. It's sort of like the problem you'll get in the back if you are short waisted and you try a too-long waisted dress. But where pants are made of stretchy fabric, it likely won't help a whole lot to try to fix by making the pant shorter. And anyway, you don't want to make the pant too short.
The fit looks fantastic in the front, so likely that's just the way these pants are, if that makes sense.
Re the shirt / vest -- you can also try a shorter more cropped shirt if you do want the shirttails to show a bit. But tucking the shirt in is an easy solution, and more amenable to what's already in the closet.