Although you've posted this in the St Pierre forum I presume you're arriving at Gillot airport in the north and not Pierrefond in the south ? So I've taken it that you'll start in the north.
For three days I would suggest driving first along the north-east coast and heading inland to the cirque of Salazie where you can find some small hotels or "chambres d'hotes" to stay.
The next day I would carry on driving down the coast and then head inland up to Plaine des Palmistes and onto Plaine des Cafres where you can find places to stay and you can visit the volcano.
From there if you had more time I would have suggested going to Cilaos but the drive to get there is quite long and twisting, so maybe it's better to just start driving up the west coast once you've reached the coast after driving down from Plaine des Cafres. Less geological features here but you'll get to see the drier side of the island and you could stay anywhere between Etang Salé and St Gilles.
This suggested itinerary means not seeing the whole of the south coast (St Philippe, St Joseph etc) as you will cross the island inland (Plaine des Palmistes/Plaine des Cafres) but in 3 days you have to choose. It's really best to visit the volcano from Plaine des Cafres, and the volcano is one of Reunion's best geological features. You could always head to Ste Rose to see the lava flows and then double back to head to Les Plaines (Palmistes and Cafres).
From Bourg Murat (the part of Plaine des Cafres with accommodation that's closest to the volcano) it's about an hour's drive to the Pas de Bellecombe, which is the end of the road/car-park of the volcano road.
From Plaine des Cafres to Cilaos is about 3 hours - about an hour down to the coast, and about 1 1/2 to 2 hours into the cirque of Cilaos.
You don't need a 4 wheel drive for any of these roads.
Distances in Reunion are always best described in time; if you take the road to Cilaos for example it's only a couple of dozen kilometres as the crow flies, but it has dozens and dozens of hairpin bends, plus places where traffic has to slow down behind slower vehicules etc.Edited: 9 years ago
If we were to follow this itinerary is it necessary to book small hotels or guesthouses in July? (4 adults & a baby)
I would recommend it as July is French school holiday period and at that time of year the island has many tourists from mainland France.
So if you don't want to take any risks (and I imagine with a baby you don't) I would definitely book.
If you don't book it wouldn't be the end of the world, but you'd probably have less choice, or find that for example places only have one free room instead of the two that you probably need.
We ended up booking a small cottage in Terre Sainte and had a fabulous time making day trips. Contrary to expectations it was very quiet with many restaurants & bars closed for the winter.
We will be arriving at Pierrfond airport 19th Dec & going to Impasse Jean Max Fort Les Avirons .We would prefer to catch a taxi or bus initially & then hire a car the following day when not so tired is this a possibility ?. We have never been to Reunion before . Grateful for any information please .