The theme’s default widgets are: Archives, Categories, Meta, etc.

Well, no, that’s not right. Those are core widgets. The Twenty Nineteen theme doesn’t have a sidebar, and doesn’t provide starter content and there are no default widgets in the footer.

4 pages for 4 types of posts,

In you mind, what is on these 4 pages? Is it a list of posts? Is it content about the type of post? Is it both? If this is really 4 categories, why make a Page? You can put a category description on the taxonomy and most themes will show it. Your menu doesn’t have to only have Pages. It can have Category links or any link you want.

Do I really need any of the default widgets?

Widgets are not the main concern of building a site. Think of them as extra ways for your user to find things. Everyone thinks differently, so your organization of content might not make sense to everyone else. It’s nice for them if you provide other ways of getting to the content they want.
Archives widget is a way to show posts by date.
Meta widget is an easy way to provide users a login link. You don’t need it if you don’t want your users to login.
Category widget is a way to show all the categories, and see posts by category.

Thank you for your reply!

As I stated in my post, I am a newbie. In the future, I’ll call them Core Widgets.

All of the four pages would contain posts w/ images. The first page would displays posts about “Art Topics.” For example, a post describing “The Relationship between Art and Math.” The second page would display posts about my own artwork. The third page would display the artworks of “Great Artists.” For example, a post titled “The Artworks of Wassily Kandinsky.” Finally, the fourth page would display the artworks of “Contemporary Artists.” For example, a post titled “The Artworks of Patty Evans” of Fort Myers, FL.

If I categorize the posts, why would I need categories?

Dr. T

All of the four pages would contain posts w/ images.

What you are describing is what a category page is. Category is how you organize your posts. You don’t have to create a Page for the category; it is already generated for you. So you just assign a category to each post, and put the category link into the menu. No extra page is needed.