Hi Katrina!
Welcome!! Sounds like you've got the tools down so you should eb scrapping in no time. Size is personal preference. I started with 5 X 7 moved to 8 X 10 briefly adn have now stuck at 12 X 12. I live in Japan and due to the humid climate and lack of A/C I'm waiting to go to print. I'm considering 11 X 11 which is apparently much cheaper that 12 X 12 or may even go with 8 X 8 which I can print myself. I recently printed some 5 X 5 and was really impressed at how good they looked.
You may also consider a coffee table book. Maya, who lives in Canada passed the follwoing link to me
http://www.bound2remember.com/
Look forward to some of your layouts