For the classic editor, a lot of people use this by way of the Classic Editor plugin, including the Classic Widgets plugin. But there are those who like the block editor because it does give more flexibility–depending on the type of content you are going to create and manage. If it’s just basic plain text, the classic editor path can work, otherwise, if you plan to create a little more details and mixed content and layouts for a post or page, the block editor will give you more flexibility.
Definitely check out the free themes and if one piques your interest try it out.
For the cost of a custom theme to mimic the example you provided, this will depend on the developer you choose. Fees can range from very little to a lot. However, look at the themes here on the .org website and choose a few of them to try out. I was going to design a theme for one person a couple of months ago but I didn’t have enough time, so I pointed them to GeneratePress. They seemed to be happy with that one. Check that one out.