Hi,

This theme supports multiple ads position:

If you use header style 3 - you can add the ads code via Customize > Logo and Header Options > Google adsense code to display in header 3 ( size 728×90 )

Customize > General Options > Google Adsense Code to Display Above Posts Layout for Archive Pages ( size 728×90 or another sizes )

Customize > General Options > Google Adsense Code to Display Below Posts Layout for Archive Pages ( size 728×90 or another sizes )

Customize > Homepage Options > Add Google Adsense Code Below Featured Slider

Customize > Single Post Options > Add Google Adsense code below post description

Customize > Single Post Options > Add Google Adsense code in the end of content posts

Customize > Footer Options > Add Google Adsense Code Above Footer 

Dashboard > Appearance > Widget > drag & drop widget "Custom HTML" to "Main Sidebar" and put the ads code there.

There is not special size, you can see all that places and see what's ads size fit with your requirements.

Best Regards,

PenciDesign