My wife wanted an Echo Dot in our bathroom. It has a sunflower theme, so I thought I'd oblige her with an attractive sunflower holder. It is pictured sitting on top of the toilet tank, but it can be mounted on the wall if preferred.
Doesn't Matter. I used 0.3.
Yes, 10% to 20% is enough
Using Autodesk 123D Design, I combined TinkeringT's "Amazon Echo Dot Wall Mount" (base2.stl) and JW1401's "Sunflower iPhone 6 Bike Mount" (SunflowerDock2-_Flowers_Version_2.stl). No scaling was required, but I did slightly enlarge the inside diameter of the sunflower to 3.3 inches.
If you want to print this in two colors (base + flower), the native .123dx file has both parts un-combined. You can save each part separately and then open them together in FlashPrint, or whichever slicer program you are using.