Great questions. You might be surprised. If you can find 30 untapped keywords in Google Search, and there's a big enough audience for topic, search volume should be fine.

Some boring topics are too small so I suggest you validate the niche first before jumping in.

In my experience, Adsense does not make very good money, but Ezoic and other ad networks can make quite a bit.

How much you make depends on your niche, seasonality, target audience, and the specific topics you write about. Most of the money I make comes from display advertising.