No additional supports needed!
0.2mm layer height.
The stl's included should be oriented in the position they are meant to be printed in. The Inner Vase has built in support. It doesn't have to look pretty where it's supported as that's where the dirt/plant is meant to go.
It's recommended that you have your printer tuned for pressure advance and flow as the tolerance to insert the inner vase into the outer vase is only 0.2mm. I recommend cutting each model so you only have about an inch of each to see if they fit together.
If you plan on scaling both models down to fit a smaller plant, there might be a little leeway, but because the two parts screw together you might not have a good time if the scale is too small as they may bind together too much.
Assembly
Vase_Inner and Vase_Outer screw together