Say, is there any way I can keep this private? I sort of wanted a place where I could organize my thoughts and ideas online. But I also want to be the one to do that. So is there any way I can keep this private? Make it so that only I can edit stuff here?
For the first, I think you are looking for "Category Exhibition". You can turn that on or off via Special:WikiFeatures
For the second, that should happen automatically, but there's some caching, so new categories won't show up for a while. If you try starting to type "browse" (a standard category) you'll see it work for that. The others should show up over the next day or so.