We will be in London for 4 days in May. Our plan is use our remaining 10 days poking our way towards Cornwall via Dorset. We'd like to pick up a car outside of London and were thinking of taking the train to Salisbury and picking up a car there so that we could visit Stonehenge and other sights and make our way to a reservation that night in Weymouth.
At the end of our trip we would return the car to Salisbury, stay overnight and hopefully get an early enough train that would allow us to get to Heathrow by around 10 am?
My questions is whether we are too ambitious both in picking up a car and getting to Weymouth and in getting ourselves from Salisbury to Heathrow. Comments and alternative suggestions would be appreciated!