Recommended to have GND plane layer for better thermal performance. Thermal pad directly going down to GND layer just under the device is the best way.
Distance between Odx to Inductance should be as close as possible. This line has switching from 0 V to VM.
FBx pin and external feedback resistor should be as close as possible. This is the analog sensing pin for the DC-DC converter.
V3p3 pin is for internal analog reference voltage, and should be quiet. External 0.1 µF should be located closer.