How many is too many?
It's only too many if YOU think it's too many. That's all.
The nicest thing about journaling is that you can have as many- or as few- as you like, and can change your mind any time.
As for me, I'm afraid I only have one. I'm just too flaky to have a bunch and try to keep 'em straight... I do, however, have quite a few indexy-type sections, like "Poetry"- "Quotes"- "FFR"(For Future Reference) and my hodgepodge of mishmosh, "The PhooBar and Grill"!