Another approach to constructing a project using proxies...
Convert large video files to smaller ones with identical names but in separate folders, as Nat has suggested.
Input your files to the timeline, loading the low-res videos but the original-res versions of snapshots, still images, etc.
Make all edits and add transitions and effects. Save your project with a unique name, so as not to overwrite earlier saves.
Now rename the folder that contains the low-res conversions.
Reload the saved project. Since it won't be able to find the converted files it will prompt to resolve them.
One-by-one, point VP to the original high-res files until all are loaded.
Export the project.