From Le Bourg d'Oisan:

day 1      cycle up Alpe d'Huez 13.2 km @ 8.1%

day 2      drive to La Grave (29.5km) climb Lautaret (easy, 11 km like Bobbin Head) climb 8 km Col du Galibier @ 6.9%

day 3      cycle up Les Deux Alpes 18.5 km @ 5.3%

day 4      climb Col du Jandri 27 km @ 9.1%. This col is quite hard but that is what you want. Asphalted up to 1730 m, then gravel up to a very                high 3151 m. Can be substituted for another climb following recommendations of fellow climbers which you will meet in great number in Oisans.

So you start by staying at the base of the most famous climb in the cycle world. The one which should be interesting is the Col du Landri, have not done that one.

day 5      rest day and driving to Jean de Maurienne, 149 km by major roads or about 85 km driving up and down Galibier, difficult to drive. Jean de Maurienne is base place for some very interesting climbs.

day 6      Col du Glandon, drive or cycle 11.5 km to La Chambre from where climb is 21 km @ 6.9% 

day 7      climb Croix de Fer 30km @5.1%

day 8      a hard one, climb Telegraphe and Galibier from the north, 35 km @5.5%

day 9      my favourite, beautiful  views of Mont Blanc, highest mountain in the Alps: La Madeleine, 19km from La Chambre @ 8%

day 10     transfer to Sault, 290 km, about 4 hours, major roads, also rest day

day 11, 12, 13, 14 - as you suggested, climb Ventoux from 3 sides. After the the first 2 climbs you may want to call a rest day during which you may want to visit the nearby Provence city of Carpentras. Ventoux generally being considered the 2ndmost famous  TdF climb Sault is well worth staying there for all 3 climbs. ( I have only done Bedouin).

Your bike rental link lists Alpe d"Huez and St Jean de Maurienne, does not list Sault, but bikes can be hired at Albion Cycles Sault. Let the guys who want to hire do their own detailed search. You will find most guys in these bike shops do speak English and can recommend the best climbs if you go outside your schedule.  

Re cars: a bit complicated because Dieter recommended something which is very good for long term lease that is more than 3 weeks. That is what Dieter and I always use in Europe but we lease cars for 2 to 3 months.

Give Global Cars, Crows nest a phone call on 1300 789 992. I find them helpful and have used them for the the last 2 leases and obtained additional discounts

The problem is that you automatically get 28 days although you do not need more than 16 or 17 days. (You  get 7 free days if you lease by Mar 31). Min seems to be 21 days, price for 21 or 28 days is the same according to their website. Go to Global Cars-Europe Car Leasing-Renault.

5 seater Espace is AUD 2899 for 21 days Code ESD, 7 seater Grand Espace is AUD 3399 for 21 days, Code GED. The 7 seater offers of course more space for luggage and bikes. One problem with leasing is that if you have to cancel say after 5 days you have lost most of your money (as happended to me after my skiing accident in 08) and you have to be lucky to get your money back from your travel insurance.

Hiring a car from AVIS or HERTZ Grenoble Railway Station is easier and more risk free, but you will not get a brand new car. I checked it out briefly be ringing  Avis on 13 63 33 Intl Reservations. You can get a 7 seater Espace or similar for 16 days at Grenoble Railway Station for Euro 1064 which is about AUD 1400. No risk - you only use it for 5 days you pay for 5 days. Depending on your risk profile you may have to take out additional insurance when you take delivery to get  insurance with no excess. They could not tell me detrails in Sydney, these additional products are only available at the counter when you take delivery in Grenoble. One of the advantages of The Renault Leasing scheme is that no excess insurance is included. On balance I would hire at Grenoble TGV station. The additional insurance to come up to no excess would make it still a lot cheaper. Or risk having to pay the excess and in case of an excess case divide the excess by 5 people.  Further information can be obtained if you want to go the route of hiring at the TGV station.  Avis does not hire bike racks but for the money you save you can easily buy a cheap bike rack say for 3 bikes and you can stick the others with the luggage in the 7 seater. If you need more info on Renault let me know as I have to prepare for my own leasing anyhow but that will be of course for about 75 days.