I have only keep a "journal" of product experiments, a copy of my product color swatches, and samples I made in classes. I bought a 9.5 x 11 clear pocket portfolio (like page protectors at JoAnn's fine art section for my journal. I am not much into diaries, journals or albums...I feel what I have in photos and on my blog is sufficient. I think it would be a lot different if I was newer to stamping.
If you read blogs about art journals people are encourage to make them in whatever way they want. Mixed Media encourages people to make art in what way the individual wants and there are no right and wrongs....and that certainly goes to journals too. Yes, spiral bound books are easiest if you are going to make art in the jourmal. Size varies a lot too. Strathmore and a couple other big art paper companies came out with new Mixed Media journals this fall...with fancy, luxurious covers (some available at my Michaels).
Some of the multi-media "instructors"strongly encourage doing some art 10 minutes a day to increase skills (the amt of time varies upward). Some folks talk of using several different types of journals at one time. Some folks are using their art and words to express their personal growth, development and/or feeling....an art diary in my mind.
The good news is no matter what you do it is right!