Scaling: You can freely scale the model in the X and Y axes to fit your specific print bed size.
Height (Z-Axis): To ensure the best look and durability, I recommend keeping the height between 1.5mm and 2.0mm maximum. Do not scale the Z-axis proportionally if you are making it very large; keep it thin for that "stencil" look.
Supports: No supports needed.
Bed Adhesion: If you experience any lifting (warping), a small brim is recommended, though it should print fine on a textured PEI plate.