Premier Elements 13
I've been working on a video by completing smaller projects. I would seem to have the option of creating one big project from all the little projects or, I suppose, rendering everything as smaller projects, then bringing all rendered material into a final version. It would seem the single project might be better?
On what computer operating system is your Premiere Elements 13 running? Have you updated 13 to 13.1 using an opened project's Help Menu/Updates? If not, please do that.
To your immediate question...
Given that you cannot import one project file (.prel) into another.
The classical way to use content from one project in other is as you have described - best keeping the project settings and export settings consistent in the projects. The choice of the export and its setting can be discussed. Some point to a Lagarith Lossless Codec.avi export. As I said to be discussed.
If your computer is Windows, then you could consider a copy/paste insert between projects. If that is applicable, then please read the details for doing this using ClipMate in conjunction with Premiere Elements.
Any questions or need clarification, please ask but include more details.