I don't think you can go wrong with either Camera Gallery or Apertures for quality service and knowledgeable sales people. I would make one suggestion, and that's to consider taking a basic photo class. Apertures offers them, but I'm not sure about Camera Gallery. You'll learn how to use all the features on your new camera and some basic techniques that will be the basis for further learning.
I learned with all manual 35mm and medium format film cameras, and began playing with vintage 35mm rangefinders a few years ago. When the time came to move up from my Kodak 1285, I chose an Olympus Pen rather than a DSLR. It has the same functions in a smaller, lighter package.
Sensor size is important in any digital camera. If you select a camera with a full size sensor, lenses designed for smaller sensors probably will not work. The older Canon EOS lenses are incompatible with larger sensors, if I remember right. The Pen uses a Micro 4/3rds sensor that's about a third smaller than a full size one, but that allows for smaller, lighter lenses. Olympus just introduced a DSLR based on the 4/3 sensor, and other companies will undoubtedly follow.
Sensor size is entirely different from megapixels. The physical size of the sensor influences the amount of noise in images as you go to higher ISO settings. Noise appears as colored specks in the darkest portions of an image, much like the grain in film becomes more apparent with faster film.
Here are some links to photo tutorials:
Cambridge in Colour:
http://www.cambridgeincolour.com/tutorials.htmDigital Photography School:
http://digital-photography-school.com/Pixiq:
http://www.pixiq.com/There are lots more. I like Cambridge because it starts with the basics. The other two presume some knowledge of photography, but they also give a good overview of the possibilities.
Please let us know what you decide and post some photos! Here's one from earlier today, for instance. It's reduced in size.