You mean Supply +ve is going to the motor, then motor to Drain then Source to ground and gate to MCU output? With a rev. biased fast acting diode (1n4001..not 1n4007) across the motor?
That's what you should have. Simple way to verify this safely is with an LED & 1k resistor as the Nfet load.
Yes u need decoupling 0.1 uf across the MCU power pins. Is your supply regulated so that the motor does NOT introduce noise onto the MCU power lines? Bad idea to share MCU power with inductive loads without decent regulation and a decent pi filter plus a sprinkling of ferrite beads and decoupling caps.