Oozak is a great place to buy your markers, or any supplies, their customer service is great and shipping is fast....they are wonderful!!!
As for help with colors and blending, two blogs that really helped me when I was starting out were Marianne Walker's - ilikemarkers.blogspot.com and Suzanne Dean's - scrapbitz.blogspot.com. Both of these offer great tutorials for coloring. Suzanne's has videos on YouTube for coloring that are very helpful and her blog lists a good starting list for color groups. These may help you out....... I've ended up with all the markers, except the florescent ones and find I now have my favorite combos for sure.......
And, I do find I like using the different gray colors for the different color groups on the color wheel. The more you play, the more uses you find depending on what you are coloring. However, lookout, these little buggers are very addicting!!!
Have fun choosing your colors and have fun coloring!!!