For finding STL files

thingiverse.com
STLFinder.com

For creating STL files I use OnShape. It’s free.
I use Cura for my slicing program.

For creating svg files I use a few apps and websites.

MS paint to clean up or edit image files.
I then use a website called Photopea. It’s free. Then to convert I use another free website called JPGtoSVG.
There is a learning curve but it’s short.

YouTube is another great resource for 3D printing and Cricut machines.