I lived in the area for years snd would definitely discourage you from driving between the towns as the roads are scarily narrow (one car width) and you end up reversing to the nearest wide spot if you're the ascending car.
Train is the only way to go. Cheap and regular.
Are you strong hikers?
The Via dell'Amore is an easy stroll, can be done with a pushchair and is nicely decorated with pictures, plaques and padlocks where the couple throw away the key. That comes from an Italian film with heart-throb Riccardo Scamarcio ( starting to look a bit pouchy 15 years on).
The other paths are hard work, sometimes only a narrow ditch, and you need hiking boots. There were several fatal landslides recently, so I hope they've one work on the cliff paths. Well worth it for the views, though. You can take a boat trip between them, too. They usually start from Portovenere. Or you could go to the Monte Parodi park and walk down to the sea (a bit easier!).
About accomodation. The villagers have a reputation for being jaded and taking as much money as possible from tourists, probably because they know they'll never see them again. So the "sciacchetrá" they sell on the street is nothing like the real thing and you're more likely to be offered a threadbare spare room than a real "Bed and Breakfast". But there are plenty of professional places, too. Booking.com is a good place to start.
I have family (IL) in Le Grazie, Portovenere and Palmaria so normally stay in that area. Da Iseo in Portovenere is our family's restaurant of choice. Palmaria is great for exploring (there's a fort at the top-Napoleonic) and they have recently opened Tino Island to tourists.
So certainly an active holiday but a memorable one, too.