1) Is it possible to have different icons on the map as it is in the popular categories at the top. The images work well at the top but not very well on the map at the bottom. See screengrabs (icon looks good, icons look poor)
This is not possible without a customization. We have an example for how to substitute different category images on the detail page.
https://wpgeodirectory.com/docs/faqs/detail-page/ (see: change category icons)
2) I have followed the instructions to allow bigger featured images on the listings page, but despite adding a max image of 3500 it is still looking blurry here.
What is the size of the image once it is loaded? Does it match your WordPress media settings for large images?
3) The mobile view of my page is look poor, can I change how the columns collapse. Ideally to go into a single listing view. See screengrab ‘mobile view’
This is probably a cache issue. Please contact your host and ask them how to disable cache on the site. Disable all cache plugins and check to see that the listings are able to ‘respond’ to mobile view.