(1) What is the best gun for beginners?
Brand doesn’t matter much. Something simple and easy to maintain,easy to manage . Before purchasing a gun ,I recommend  trying some out . Ask a lot of questions. For instance;
 1) Over and unders are easy to maintain ,but getting one of good quality are more expensive.
 2) Semi autos are softer shooting , but more trouble to maintain and must be chosen for the purpose at hand because they can be finicky about the ammo.But can be very versatile.
 3) Pumps are easy to maintain , much less finicky about ammo much, less expensive and much more versatile for purpose.
 Versatile being , if you don’t like the barrel length ,another can be purchased and installed without any special fitting. If you want a different stock configuration same thing , no problem.
  Also gauge. 12 or 20 gauge ammo is more available for many purposes and recoil reduction.
 12 ga being the better of the two.
(2) How much do you lead the target?
     There are several ways to acquire the target and also many angles and variances . The best thing is find a good instructor or coach . They can make this a very simple process.
 (3) Do you shoot with one eye open or both?
  It is usually better to have both eyes open, but some people can not do it this way.
 (4) How do I know if my gun fits properly?
  1) Does it hurt? Shoulder,cheek ,arm etc.
  2) Pattern test for point of impact.
  3) Are you looking directly downthe rib or barrel?
  ** note ** These things could also come from an improper mount.Best advice Shooting coach or gun fitter