Creating models for beginners

[Geo]

@crackersjv

Is there a recommended free plugin to perform that function?

Yes, there is. See this topic:

Performance differences using flat colour materials or jpegs

A texture image will weigh more on file size and performance than a simple material color. But if you keep the texture image size to a minimum you shouldn’t have any problems. Here’s a quick example made with @TIG 's Image Trimmer plugin. Beer.skp (1.4 MB) Experiment with it. Try making an array of, say, 2500 of each component; 7500 total instances. I found the model still performs quite well. You may want to turn off the shadows first. More about Image Trimmer in this topic…

And here’s another method:

Create a 3D model from raster line art with help from Adobe Illustrator

Have you ever found an image or even made a quick sketch (the old fashioned kind) and wanted to quickly make a 3D model out of it? If you have Adobe Illustrator and SketchUp Pro, here is a quick way to do that. Place your image into an Adobe Illustrator document. From the toolbar select “Image Trace” OR select the Image Trace dialog from the Illustrator Menu Window > Image Trace Adjust the Image Trace settings. If you are just looking for flat shapes from line-art (or near line-art) ima…

There are recommended free learning resources as well.

Given the description of what you’ve already accomplished…
Investing perhaps twenty minutes in learning would enable you to create what you want.

That is, simply trace the outline of the stencil and then erase what you don’t need.
Then extrude it to 3D.