Don't pay it all up front, and don't agree to do so. If you are absolutely, flat-out broke, you should still be able to pay something, even if the artist hand waves and doesn't want anything for their work. Be good to your conscience and at least ask if you can make a small donation to one of their three favorite charities.
If the covers in your genre's section of the bookstore are all orange, should your cover be orange, too? It's hard to say. You want it to look like it belongs in that section, right? But you also want it to stand out. I would say, if you are a new author and you are predominantly selling online, you need to consider how your work is going to look when it's shown with others in the genre.
Never, ever use the word 'by' unless you are referring to an 'edited by' line. Otherwise, just use your name as the author name. Don't believe me? Go to a bookstore or Amazon and look at what's out there.
Yellow is a vibrant color but it is rather difficult to see against a white background. If your cover is mainly white, yellow is a poor choice for author or title lettering unless you outline the yellow in a darker color.