The most important thing is here whether page rendering is blocked by the image download (or if the page is incredibly ugly or unusable before images load). In your specific example the rendering isn't blocking anything (though the text shifts a bit for me in Chrome).
It's important to note that images generally don't block the loading of the interface in HTML; the HTML document and CSS are loaded first, so images don't block much of the initial page render. IF your image dimensions are specified in the HTML there should be very little redraw upon loading of images.
Watch your loading times; loading time directly affects bounce rate. If possible A/B test and see if no/smaller images and faster loading leads to a better bounce rate. See also my answer here on loading times.
There's no set size, but smaller is better in general of course. Ditching images is a very quick way to boost the speed of websites, though in the case of a landing-page image, dropping the hero image is often unwanted; if you don't show your product/service/item of interest at all, it might not make a great first impression after all.