One of the articles has a link to a freelancer calculator to help you determine what you should be charging per hour. Perhaps not an ideal calculator for an artist (I use a $ per square inch formula for my work) but very helpful to see where your costs (expenses, personal) really are. Here is the DailyWorth article and here is the link to the calculator on FreelanceSwitch.
If you are not subscribed to Netted you should be. This daily mail gives you a heads up to some pretty interesting sites that you probably would never find on your own. DailyWorth was one of their recommended picks. Netted covers all topics from the fun (games, photo editing, etc) to the more serious (calendar, business apps, information). I don't always follow the links from every day, but it is interesting to see the creativity of other people as they fill niches.
There are many wonderful sites out there and I think DailyWorth and Netted are two that should be on your "to visit" list. Netted has an archive and search feature in case you missed or deleted an email.