It is essential that the catcher is able to receive, block, and throw from the same secondary stance. The specific width will vary with the catcher, but a good frame of reference is roughly shoulder width apart. Again, athleticism to execute receiving, blocking, and throwing is the essential factor in the secondary stance.
The right should should be slightly offset and behind the left foot. This will help with the Two-Step Footwork for throwing. The catcher should be careful to keep their chest open and facing the pitcher so that he/she is presenting a good consistent visual for both the pitcher and the umpire. This will also ensure that the catcher can block the ball well. If the whole body gets twisted too much then the visual changes and it will be harder to block.
This stance is taxing on the legs but that’s the way it has to be. The butt should be up with the legs parallel to the ground to allow for maximum explosiveness and quickness. One tip is to shift into the secondary stance as the pitcher begins his/her delivery. If the catcher gets into this stance too early then the legs will get tired before the pitch is delivered and it will cause unnecessary fatigue in the legs.
The target is the same as the primary stance. The catcher must always be focused on winning pitches by presenting them to the umpire in the best way possible. Winning Pitches is still the most important skill in catching so the secondary stance should still allow the catcher to receive pitches well.
Some coaches will say that this is a vulnerable position for the hand, but if the catcher keeps the hand tucked into the hip then it is safe. This hand position allows for the catcher to receive, block, and throw most effectively because it puts the hand in the closest possible position to either get into the proper blocking position or execute a transfer quickly.