Have you seen good resources / examples to build a 'mini design system'?
Looks like most of the content about this is made for larger design teams (>20 designers)
Not really... When I'm making a "mini design system", I just create a Figma file with the colors, gradients, shadows, components and typography. I think this is enough to use in a smaller project and you don't have to make it fancy or anything. Just put things there in a way a normal person can understand and that's it.
My suggestion is: don't overthink it. If it's not a big project (yet), you can just use your intuition sometimes.