a. The clothes that the subject is wearing suggests a more wealthy background, with the puffed sleeves, thick band necklace, and flamboyant hat. However, the colors are not especially vibrant, and seem to show modesty.
b. In the background, it is just a dark wash of blue, which puts the attention on the character, which then puts more focus and the lightest part of the painting, his face. They might be an important figure because there is nothing excessive in the background, as if all they needed was a portrait.
c. The artist wants the viewer to feel as if they are looking at someone important, since it puts more attention on the actual person, and his clothes seem to mark him as someone who can spend money and time on something opulent, like thick necklaces and frilly hats.
d. The portrait is of Johann Friedrich the Magnanimous. He was the elder son of John the Steadfast, and was relatively well-revered. Johann was a calm and relatively pragmatic person. He liked his father, and deeply tried to follow in his footsteps. He cared about what the people thought.