Recommended post image in Adventurous Pro

Hello! I started to build my new site with the Adventurous Free version and read (somewhere...apparently not correct?) that you need the following sizes for images: Post - 778 x 438 Featured Grid - 800 x 600 Featured Content - 400 x 300 Featured Header - 1300 x 514 Featured Slider - 1680 x 720 I have just bought and downloaded the Adventurous Pro theme and I see in the theme instructions that there are sizes for only three image types. The Feature slider, 1600 x 600 The featured image in homepage, 800 x 324 instead of 1400 x 514 and the small thumbnail is 400 x 267. My questions are: 1. How big should the featured image in a post be? 2. How big should all the 'normal' post images be? 3. Do I need to change my existing images which are all of the sizes listed in my first list above? Thank you for clarifying this. I've searched but can't find any mention of it anywhere... I don't suppose it's necessary but just incase, my URL is https://exploreandalusia.com Thanks.