Firstly, to the forum
Problem is bud... Dartmoor is a large landscape with vastly varying terrains & weather, ancient forest one minute, barron moors the next, so it really depends on where your planning on staying the night.
Do you have a set route & a rough idea of where you'll be staying overnight? (you don't have to post them here... I'm just wondering if you'll know beforehand what environment you'll be in).