First off, a shotgun is pointed, not aimed - unless you are talking about shooting it like a rifle with slugs.
The butt stock goes into the pocket between your shoulder and collar bone, THEN you may need to slightly lower your head so your cheek rests comfortably on the comb. If you have to mash your head down with a lot of strain and you mash your cheek down hard on the comb, the stock does not fit you. If you are seeing the rib and not just the bead, your comb needs adjusting otherwise you'll be shooting too high.
Yes you keep both eyes open - that gives you depth perception, just like a pistol. Your eyes are the rear "sights"
You might try going to a trap/skeet club and explain your newness to them. Most places always seem to have an old stalwart around who can give you some basic pointers and correct some misconceptions.
Do NOT stand perpendicular to your target like hi-power rifle shooters do - you won't be able to move with the gun successfully.
If RH, stand square to your target area, your left foot should slightly more forward than your right, both about shoulder width apart and toes in a 10 and 2 type position - it should be a natural and comfortable stance, don't overthink it