Driving is the easiest way by far to explore Otaki, and the Kiso Valley in general (not to mention most of rural Japan).
Rental cars are available from JR Rent-A-Car just outside Kiso-Fukushima Station:
When checking availability at the link above, under Pickup Office, choose Koushinetsu from the area list. Then under the Office List choose Nagano: Kiso-Fukushima
Mountain bikes and e-bikes are also available for rent at the Otaki Village tourist office. When the weather’s good, an e-bike can be a great option for accessing the Ontake Pilgrimage Trail.
If you stay over, your accommodation can often arrange lifts within the village.