Does page layout / UX matter in SEO?

I can answer as far as Google is concerned and I would suggest Bing is the same. Google does not just fetch the source of a page and index it (the HTML), it actually renders the page just like a normal browser would. Therefore they fully understand what is displayed on load and what is below or hidden. This is typically referred to above the fold content.  

Its been a long-held belief that content above the fold will be more important than the content that is hidden or below the fold.  This does not mean the other content is not indexed but the content appearing within the above the fold area is given priority. 

On June 19, 2012 Google rolled out a page layout algorithm which was designed to put the users first. For example, Google uses this Algorithm to find (and downgrade) websites who have loads of adverts above the fold. 

More about Google's page layout algorithm here: https://www.sistrix.com/ask-sistrix/google-updates-and-algorithm-changes/google-page-layout-algorithm-update-ads-above-the-fold/

On June 19, 2012 Google rolled out a page layout algorithm which was designed to put the users first. For example, Google uses this Algorithm to find (and downgrade) websites who have loads of adverts above the fold. 

More about Google's page layout algorithm here: https://www.sistrix.com/ask-sistrix/google-updates-and-algorithm-changes/google-page-layout-algorithm-update-ads-above-the-fold/

Yes 100% - even high quality images over stock images matter.

It its a better UX it will rank better.

RankBrain takes care of most of that anyway but there is an additional algorithmic layer that also handles UX.

Googlebot is now an evergreen crawler. Still be careful with AJAX though!

Yes, even high quality images over stock images matter.