How to remove 'old' Premiere Elements files just taking up space?

Hi,

INFO

Windows 10 64bit

The usual default installation of Premiere Elements 2019 (UK)

My projects are being saved in C:\Users\Pete\Documents\Adobe\Premiere Elements\17.0

My current project is called Irene.

As expected, each time I save my progress, I increment my project, and note that PrE creates project files in C:\Users\Pete\Documents\Adobe\Premiere Elements\17.0 called Irene1.prel, Irene2.prel, Irene3.prel etc.  I am now up to Irene10.prel and have run out of space - hence the need to delete versions 1-8!

The source files I need to build the video are all in folders in D:\AdobeProjects\Irene 2018

BACKGROUND

I'm just getting started with Premiere Elements 2019, and I'm gradually working my way through some of my lack of knowledge issues.

So my question relates to how to safely remove old user project files I don't need to keep.

This was prompted by a 'File importer detected an inconsistency in the file structure ' error message which was quickly traced to a full C drive.

This was the result of an intensive few of days with my project, and, because I was saving my progress at regular intervals, I did not notice the space filling up the drive.

I would like to keep the current folder arrangement, just keep Irene 9 and Irene 10.

QUESTIONS

1.

So firstly, before I just simply delete C:\Users\Pete\Documents\Adobe\Premiere Elements\17.0\Irene 1.prel, Irene 2.prel, etc..I want to know if itis safe to do so, or will cause issues.

2.

Of course there are other folders in C:\Users\Pete\Documents\Adobe\Premiere Elements\17.0 :

Adobe Premiere Elements Audio Previews

Adobe Premiere Elements Auto-Save

Adobe Premiere Elements Captured Audio

Adobe Premiere Elements Captured Video

Adobe Premiere Elements Video Previews

Encoded Files

Layouts

Media Cache Files

Peak Files

Score Files

Styles

I do not yet understand the purpose of these (except Media Cache Files), however I want to be clear about what if anything I will need to delete in these folders if I only want to keep my projects Irene9 and Irene10?

3.

My thoughts are that (after deleting old versions of a project) I would like to aim to keep a seperate backup of the source files and final created project so that if changes are needed to a project - even after a few years - I would still have retained the original material and PrE files.

I hope then I would only have to make changes - and not have to start from scratch.

Assuming that I reinstall PrE2019 in a few years to work on an old project, what do I need to backup and archive? I would backup the source files obviously, but 'what and where are they' other files?

PS

I am aware that there is 'another method' of changing PrE so that it is changed to save everything belonging to a Project into individual Project Folders - and I might come back to this method - but for now I would like just to stay with 'where I am up to in my learning'.

Thanks for any helpful advice guys

Pete