Hi Philippa, here are those answers..
1. In 18 tags, can the home page have two invisible columns and when you click on the image so that it links to, for example, job vacancy information on one side and click on a separate image to link to candidate information on the other? If this is possible, how?
You’d need to look at the plugin for this kind of functionality. The theme doesn’t do anything like this (the theme is just the design)
2. Can’t get the mega menu to work – would it be because I don’t have enough subdivisions?
Yes the might be the case
3. I don’t think you cover the colour of the bar where the social media icons sit …
You can change the color of this by changing the color of the secondary navigation background colour