What are the key considerations when determining the route and course design for a gravel bike event, and how can organizers balance the need for challenging terrain with rider safety and logistical constraints? Are there any specific tools or resources that can help with route planning and course design, such as software or consulting services, and what are the benefits and drawbacks of using these tools? How can organizers ensure that their course design is inclusive and appealing to a wide range of riders, from beginner to advanced, and what are some common mistakes to avoid when designing a gravel bike course?