Slider Image Size & font colours

I am re-styling my sons website at www.mattfurness.co.uk. Three queries please; 1) I have used images sizes 1920 x 1080 as featured images on pages, to be used on the home page slider. However the images appear to be too big as they do not automatically include the social media icns at the bottom. Am I better using a different size? If so please advise the best size. 2) As you can see the white font on the home page does not work with all the images. Can you advise CSS coding to change the colour of site title and description, and also title and wording in the slider please? I can then play around to find the most suitable hex code to use. 3) Also CSS code please to change links from an underline to a diffrent colour for the text. Many thanks. I appreciate the work gone into this theme. Chris