First off, why are you on a 157? Especially with the flying V profile, you should be riding around a 153, and if your feet are big you should be riding a wide board so you don't have to ride something so long. A shorter board will be more manueverable (smaller radius, which means quicker and/or shorter turns). Also, the longer the board, the more weight it takes to cause the board to flex which causes the board to turn. You're only 140 lbs, so a 157 will be harder for you to control. For me, 5'10", 180lbs, size 10 boot, a 157 is the longest board I will ride, even for a deep day in the backcountry as long as the 157 is a reverse camber profile. I will ride boards as short as 152 but a wide model to keep the toe and heel drag down.
Next, the width and angles of your stance will completely depend on your terrain riding preference and personal comfort. A wider stance offers more stability on boxes and rails and jumps, while a narrower stance is more ideal for dynamic carving and holding an edge on ice or in a halfpipe (a narrower stance will cause the weight distribution of your body to be more directed toward the center of the board which will make it easier to flex the board and turn).
The angles of your bindings is really more what is comfortable for you. I personally ride with my front foot at 15 and my back foot at -12. I ride a lot of switch and for some reason -12 is just more comfortable for me when riding switch. It would be harder to ride switch if you had your front at 15 and your back at 0, so keeping the front and back foot angled withing 3-6 degrees of the same would be helpful to riding regular or switch. Also, riding with your feet at angles can help reduce toe and heel drag.
Look at profiles of a bunch of different pro riders and you will see major differences between them all in their stance width and angles. You'll see some trends between the riders who all ride park only and street vs. the backcountry guys, but then sometimes you'll see a backcountry guy riding their stance like a park guy. It really comes down to you and what feels good for you. If you feel like you're getting hindered then change it up a little and see how that change works- better or worse. Good luck