Each adsense ad has unique 'ad_slot number'. So, can I use the same adsense in the same page at 2 different places? Also one under another? Or Do I have to use 2 different ads with different 'ad_slot number' ? Someone clarify. Thanks.
You can use the same ads but that way the results will only show in one channel which is not good if you want to track the performance of your sites.
No TOS issue but using different channels will allow you to track the performance of ads placed at different locations on your page.