Know when to wait. Some affiliate programs require a certain level of traffic, subscribers, etc. If that’s the case, I say it’s better to wait to apply for that program instead of applying and hoping for the best. You risk being labelled the person who can’t follow guidelines and you might also risk not be allowed into the program when you do meet the qualifications.
Next, you’ll want to pick a WordPress theme from somewhere like ThemeForest, Elegant Themes or OptimizePress. This is the barebones design of your site, which you can then customize with your own branding, copy, and images. That being said, you don’t want to cheap out. It costs less than $100 to buy a theme that will make your website look professional (and you can upgrade to a completely custom design once you get the business going).