Parkour athlete Obsidian 1138 launched one of his already famous videos, full of great workouts. The exercises demonstrated in this particular video do not represent a full workout routine, but just a collection of training ideas the team at Nirthen Parkour put together for you. You can use these to complement your Parkour training.
As for the intensity, as with any training, it should always be challenging. As long as it is, you should see gradual improvement over time. Obsidian suggests that you set yourself training goals and work towards them.
When working to build strength, you need to also consider diet, as well as the actual exercise. Nutrition and is an important part of any training regime if you want to benefit fully from the workout.
Check out the strength training video: