Google Web Fonts are great for premade themes and DIY web projects. They are easy to install and give you a lot of options. When I design websites, I often use no more than two fonts – for consistency and cohesiveness throughout the site and to keep page loading times at a minimum. I stay away from using Google Web Fonts for custom branding projects, because I am a big proponent in customization of all elements of a project, including the fonts.
Pairing fonts is a great way to provide a visual hierarchy to your content – clearly delineating primary and secondary information. At a very basic level, you can create a font branding board for your headings, subheadings, paragraph, and smaller accent text like in the mockup above. A mockup branding board will keep you consistent when you are designing and developing blog content such as collages. If you find a pairing that you enjoy, when it comes time to designing your blog, you can provide your designer with these fonts!