heathrow-devon-scilly advice

Hi. I am planning to land at Heathrow in early June and have five days to kill and instead of doing the usual in London, I was thinking of taking a train to Devon, rent a car in Devon, staying for three or so days and then heading out to spend a night on the Isles of Scilly. Then drive back to Devon, and train back to into London, where we are meeting friends.

Some questions:

1. Doable? Enjoyable? Looking for relaxing, quaint town, good food.

2. If not, other alternatives?

3. Suggestions for places to stay, train and rental car tips?

4. Food tips?

Thanks in advance.

NR