How many ad units are enough for a website?
If you have several ad units on your webpage, it is most likely that the first one or two will summon all the unique impressions, and your other ad units will become inactive and display only free affiliate ads.
This is exactly why we recommend our publishers to make good use of one or two banners per page. You can follow our rules of ad unit allocation.
Honestly, filling the page with ad units will hardly make you richer, this will only create excessive load on our servers.