Most power wheels come with a spoked wheel assembled to the motor. You buy a power wheel kit with controller, brake handles, throttle (legal here) and optional display. Brake handles shut off the motor if you brake, also if the controller fails full current, which can happen.
Read the nominal tire diameter off the tires and buy a fat wheel kit to fit that tire size.
The controller voltage has to match the battery that you buy.
As you live in Ireland, i have no suggestions as to a reliable supplier. Euro rules are pretty strict, so buying in China or HK is likely to get your purchase confiscated at the border. Try to look around for a European ebike forum.