is it better to keep all the props in one large mixin?

If your component library is not constrained to using Vue 2 you might want to take a look at Vue Composition API to share functionality (methods + reactive state) between different components.

Mixins might not be what you really want to be using because you kind of lose information as to what features/props/methods really will be put inside your component without re-checking the mixin code. You also might run into issues when component options get merged by Vue at runtime. Check out these posts for more information: https://css-tricks.com/how-the-vue-composition-api-replaces-vue-mixins/ https://reactjs.org/blog/2016/07/13/mixins-considered-harmful.html

As for sharing props: What I’ve seen just yesterday (but not yet tried!) in a talk by John Leider – creator of Vuetify – is create a function that returns the props you want to reuse between components. Then you just call said function inside your props definition and use the spread operator.