Hey, If I put Adsense in my WP posts (index.php), the adsense ads will be added to all posts on the front page (but ofc I can only see the first three). Is Google Adsense okay with this or should I remove them? Or is there a way where I could only put them on the first two or three posts?
You can display ONLY 3 standard adsense adblocks. I advise you to remove ad code from the WP index.php as trying to display more than 3 ad blocks on a same page in against Adsense terms of service.
You can place 3 ad units in one page. If you place more ads, then only 3 ad units will be active, not sure if google mind having more than 3 ad codes in a page as google simple do not show more than 3 ad units. You can find some plugin to show only 3 ad units, I personally put ad code manually in templates so I do not have this problem.