Sure, breed like crazy. Food is free, and you can always sell the fish you don't want. Each tank holds 20 fish. As for the log, I think it's more fun to start keeping one yourself. I did that, and filled it up in no time. Keep two logs... one for breeds, and one for fin types. I am still adding to it every time I play.
Advertising is important, but not as much as researching Fish Environment. That is what helps you progress along the fastest.
As for price of fish, experiment a little. If a fish doesn't sell within 5-10 minutes, it probably won't sell at all. Lower the price a little and try again. Under the right circumstances, you can sell some fish for nearly double their suggested price!