Previously Adsense only allowed 3 Ad unit and 2 links unit per page.
But as at September 2016 Adsense changed their policy, allowing an unlimited number of Ad units on a page.
It's also important that Advertising and other paid promotional material added to your pages should not exceed your content.
you can also place unlimited Link Units as long as the adverts are not exceeding the content.
It is important your site's quality is maintained.
It is also allowed to add ads from different Google Adsense accounts.
AdSense stated in their policy:
“We may limit or disable ad serving on pages with little to no value and/or excessive advertising until changes are made.” I suggest you keep less than 5 ads per page.
It's better to stick to 3 or 4.That's all please share