For me, I usually just start with reference stance and ducked +12/-12. I personally don't make much adjustments to my stance or angles when riding different boards, but I don't ride super directional / powder boards since there is never any powder where I am. I also love to ride some switch, and actively practicing to improve in that area. You don't need symmetrical angles for switch, but duck stance is good for switch riding.
tbh, I think reference stance is usually fine (but your board may to a bit short for you so the reference may be a bit narrow). You are usually just looking for slightly wider than shoulder width stance. For someone who is 5ft 7in, I would guess probably 20 inch width stance as a starting point. Another common way to get a starting point stance width measurement is measuring the the length from your kneecap to heel. Make sure the stance is centered off the reference stance to start with. There is no absolutely correct stance width, it's variable on personal preference, but I would try to stick closer to about slightly wider than shoulder width as a starting point rather than something really extreme. I don't think there is any need to fiddle around with stance width that much, as long as you feel comfortable and stable and balanced on your width, it's fine.
While it seems like there are infinite set-ups for angles, I think it is really just picking between a comfortable duck stance vs more positive stance to start. I wouldn't really make any adjustments until after a few days of riding, and then only a very small angle adjustment at a time to really get a sense of the differences.
For angles, I personally ride duck stance, and I think starting out somewhere in the 12-18 degree range duck stanced is a good starting stance (example +15 -15 is a common starting point). Just stand in your snowboarding stance and see how your feet are angled. You can decrease the back foot angle slightly if you like (since you don't ride any switch), but I think you should definitely try to learn to ride switch!! It will help your overall technique with regular riding as well a ton, and I found while riding switch you really focus on technique and make a lot of improvements with your riding.
A lot of people ride with both positive angles & only in one direction, but I think that is a bit of a different riding style and it limits your progression if you don't do any switch at all. I think it is helpful to ride some type of duck stance for a little bit and get comfortable with switch riding on greens at least before switching over to full positive one directional riding. Full positive angles you can leverage your back knee a lot more inward/outward for your turns, but when ducked you are usually relying more on your front knee and pedaling with your feet for torsional twist and I think it is really helpful to develop the habit of using your ankles and torsional flex of the board for fast turning. I think riding a bit of duck stance does help with technique prior to switching over to full positive angles. For example, I recently saw someone riding a narrow board with a narrow dual positive stance with really straight legs, and I think his technique would have benefited from riding a bit more duck stance and switch. But end of the day, mostly personal preference and what you want out of your snowboarding experience.
Finally, I think it is best to stick to one set-up to practice with rather than constantly adjusting stances/angles too much. If you are switching set-ups too frequently, it is hard to improve as a bunch of other variables are changing. While stance angles / width can impact your riding, as long as you are not in a weird set-up, you can learn and progress on a wide range on set-ups, a lot of it is more personal preference. I wouldn't worry about it too much after you found something comfortable. If you switch set-ups, ride a few days on the new set-up because it takes your body some time to adjust. Usually, it is more fundamental technique issues rather than stance width/angles that are hampering riding and progression.
Getting the Burton EST tool (EST® Tool | Burton.com Winter 2023
) or a similar pocketable screwdriver is helpful if you are playing around a lot with adjustments while on the hill. I always carry one in case my bindings need adjustments.
Hope this helps and good luck finding your set-up!
edit: also, another important factor that wasn't mentioned is forward lean! I personally think a good amount of forward lean is very helpful in keeping your knees bent and shins forward in proper snowboarding posture (also really helps with carving keeping hips forward on toeside turns and getting more leverage onto the heels for heelside turns). Extra forward lean usually helps most people's riding (only exception is if doing a lot of park stuff, may prefer to have less forward lean).
edit2: another thing I thought of. if you are on an unfamiliar board that is a bit short for you, you may be compensating or riding slightly differently than normal without noticing. it may be helpful to do one quick group lesson to see if an instructor can spot something that can help or can ask someone to film you, and post on these forums.