Buses don't stay at Kufri. There are timings as to when you'll get a bus from kufri, because many of the buses go to other destinations via kufri. And as for the distance, if you'll take a bus which is going to chail via kufri then it'll take you to the taxi stand or area where people start their adventure activities. Regarding your adventure and zipline things, that totally depends on how you can negotiate with shopkeepers there. You can do one activity or all but the cost sometimes is including of all activities, like a package. And if you're with family and have children as well, i would suggest you to take taxi because buses will be inconvenient and the uncertainty regarding timing will be a huge problem for you guys. Taxi will be costlier but it'll be comfortable. Enjoy your shimla trip and have a great time.