Reduce projects file size

First of all, the size of the raw cptx-file is not that important, it is the file size of the published HTML5 output that you need to watch more closely. You can have an estimate of that output size by using the Check button in the Project Info panel (open from Windows menu):

For the same reason I would never delete unused items in the Library before the project is finished. Sometimes the  'unused' files are not correctly reported (when used in states by example).

Are you really in need of disk space in this time of cloud storage? Strange... nowadays I always have too much space on my disks.

To reduce file size for both cptx-files and output folders:

• Never resize media assets in Captivate (graphics, video) but use a dedicated application to import the media in exactly the size you need them. FYI: the Adobe Media Encoder is packaged with Captivate if you need to reduce video size.
• For video and audio choose settings to have an acceptable quality. Examples: do not use Stereo for narration, do not use 8K video, choose a bitrate as low as acceptable for quality.
• Reuse where possible: use shared actions instead of duplicate advanced actions.
• For audio import uncompresssed wav files, let Captivate do the compression to MP3 on publishing.
• If appropriate use SVG instead of bitmap images. 

Forgot to answer about the cpvc files. Did you import them as raw cpvc-slides? In that case they are in the Library. I would prefer not to delete them, but certainly not if you imported the published mp4 from a cpvc project.