How many days do you have and hopefully you have transport?
As Nod said traffic will be heavy in August - the worst days are when it rains as everyone just goes out for a drive.
Powderham Castle has a Castle (surprise) and also a deer park at Starcross which can be viewed from the cycle path beside the railway line parking
here.
Haldon Belvedere is a bit of an oddity
here
Mamhead Obelisk and the Haldon Forrest have super views, the Forrest doesn't offer a great deal due to density of trees but the road up through from Starcross has some opportunities to look across the Exe Estuary around
here
The whole of the Exe estuary and Topsham village RSPB at Bowling Green Marsh is nice
Cockington village between Torquay and Paignton for thatched cottages.
On Dartmoor I can recommend a Lunch or Dinner at the Rugglestone Inn close by you have Buckland in the Moor for more thatch which can be included with a Stroll up to 10 Commandments Rock at Buckland Beacon or Emsworthy Mire and Saddle Tor with a very much photographed
Tree just behind it which is probably best visited in the evening light, whereas Combestone Tor is ok at both sunrise and sunset and is very close to Venford Falls.
A good energetic walk would be to start in Paignton and follow the coastpath around to Brixham with a Bus ride back.
Torbay Steam Railway can be viewed passing at various angles on the South West coastal path between Goodrington and Broadsands Beaches which has some large Viaducts at Broadsands. Brixham town and Berry Head Fort and quarry.
Or you could ride the steam railway and take in a bit of Dartmouth.