Wow, that's a question that's gonna require a web site all its own..
Hand placement is usually a sign of contact confidence. And that placement, and speed at which they move, is dependent on your perception of an incoming ball, your hand -eye-coordination, and your recognition of picking up the pitch as far out in front of the plate as possible. Tall order hugh?
Good pitchers who have studied the art of hitting just as hard as the art of pitching understand these relationships.
Ok, now to address you question(s) directly. More often then not, your answer first depends on your physque - are you tall and thin, compact and stocky, or average build. Each of these .. body types.. will dictate how you move and to what extent you CAN move. For example, if your stocky, your mid section.. or girth as coaches like to call it... will only allow you to do so much, regardless of how quick you are with your hands and any associated bat speed(s). So if your stocky, and your hands are held down between you your rig cage and belt line, you'll have a swing that ranges from flat out over the plate .. to a upward swing and the end of your arch.. after the plate. Now if your really tall and thin, your hands will more than likely be high, near the ear flap on your helment. In this case your swing is going to be dictated by th brittleness of your ending arch of the bat as it crosses the plate (know as your swipe path) and you'll more than likely golf the ball... due to the high percentage of low and away pitches that you'll receive.. in addition to curve balls and sliders.
With respect to your elbows, elbows are usually a sign of your pitch preference - regardless if this perfernce is deliberate or not. In other words, batters that are power houses like to their elbows back and tucked in just a bit. Hence, when their ready to send the ball into the lights they use their trunks (mid section) and hips to "charge" the way and the arms and wrists-- supported by the shoulders.. finishes the job of contact.
On the other hand, elbows that are spread open .. front elbow pointing towards the pitcher... rear elbow pointing towards the backstop , are prone to the inside pitch due to their lack of bringing the sweet spot of the bat IN far enough to make any quality contacts.
Cecil Fielder had a unique signature to his elbow placement. Th front elbow was pointing straight down at his feet and the back elbow was pointed directly back.. flat out. This gave Fielder an excellent posture to hit the sinker. Orel Hershiser, one of the great sinker ball artists of his day found that out every time they faced one another.
I hope my answers here helped you some. If not I can expand on this very complicated topic a little more. And on a final note, you can learn a lot by watching MLB games on TV and notice the batting styles of the guys that do this stuff for a living. i would suggest taking notes of body builds, arm and hand placements, and their feet placement in the box. Then make a judgement of your observations... what did they look like and how did they perform.. or not.
And of course, bat weight, bat length, barrel size, neck size all contribute to this complicated equation. THAT by the way is why I'm a pitching coach. The art of hitting is just TOO MUCH WORK!!