The answer is dependent upon loads of elements that one sentence reply is not feasible. However, I put forward you to A/B test the ad units, ad sizes, and ad types on your webpages. Say, you add 4 ad units on 50% of your webpages and 6 ad units on anything of 50%. Monitor the page RPM of these pages to assess the profitable number of ad units. You can do an identical for ad size and layout.
AdSense offers the experiment feature. Take it slow to check it >> Add ad testing to your apply to see better results. Take the help of ad operations if earnings optimization is required.