Confusion over project size growing

FCPX 10.2;

I would like a little guidance regarding the media in my test project for learning.
The imported media is Panasonic AVCHD and is stored external to the Library containing the project.
An Event contains the clips for use and in the library bundle are shown as links.
As soon as I have placed clips in the Timeline and done some tests with Key-frames, Holds and Masks on secondary Timeline clips, the project has grown to some 75GB for some 45 seconds.

The project bundle now has an additional folder Render Files with very many High Quality Media folders such as FB7.... all showing different dates and times. These appear to contain data on sets of frames and are many MB each.
I have a 'feeling' that some of these should be deleted as editing proceeds.
The Inspector Info says I am using Original Media.

Have I overlooked some housekeeping and if so I would be grateful for advice.

75GB seems an enormous amount for 45 seconds. What are the project properties? What did you select as the render format?

If you assign the cache to the external folder the render files will be in there. Regardless 75GB is way higher than it should be, unless you've been constantly making changes and re-rendering. Personally I would recommend switching off background rendering.

in addition to what Tom said, check support.apple.com/kb/PH12704?locale=en_US for information on render files and how to delete them.

Thank you both.
The properties are 1080p rendering to ProRes 422 which I suppose could be changed to LT.
The rendering is quite fast to SSD so was not a problem, but size is.
I have been making many changes due to freezing periodically such that I have to reboot and then discover some of the Key-frame parameters have changed. I also had a problem with auto Key-frame (I can't turn it off) producing multiples every time I changed the parameters (perhaps the position on the timeline moved a hairsbreadth?), so constantly editing... Oh for an editable key-frame list!

I have briefly read the article from the link which suggests several useful options especially as this is not a real project and I am learning.
There are 585 of the folders mentioned, you can see I had a lot of freezes.

I feel sure that matters will now improve by turning rendering off or deleting periodically, and thank you for your input.