If I start a new project using the blank template, and I later decide the features of the fiction template would be more useful, can I change the project type?
There is rarely a need to do that. You can refer to §5.3.2, Converting a Project to a Different Template, pg. 76 in the user manual PDF for further information—as well as helpful links to other sections on copying settings or moving items around between projects.
“moving items around between projects”. That excites me. You’re saying I can actually merge sections from one project into another project?
And easily, at that. 
You just open both of them and drag and drop—and for big merges there is an import command in the file menu.