MiniComps makes a great UI for manipulating p5js sketches.
Here, just controlling the size and rotation of a primitive 3d object.
Sadly, it does not seem like you can use an external canvas with p5js. You have to use the one it creates with the
createCanvas function. You can reparent it though, and with a bit of CSS, you can make it play nicely with the MiniComps Panel.