Q: Should I buy a scope and camera or a long lens?
You don't buy a scope to take pictures of birds. You buy a scope to look at birds. That is what it was made for. You carry it the field while birding to look at birds. If you have an interest in photography as well, you can attach a camera to the scope to take pictures of birds. It is a lot of fun, will produce some amazingly satisfying images, and adds very little weight or expense beyond what you are already carrying. And, you can take photos of the birds you see from fairly long distances, casually, without much special effort beyond attaching the camera. That's digiscoping.
You don't buy a lens to look at birds. You buy a lens to take pictures of birds. That is what was made for. You carry it in the field while photographing birds. That involves a whole set of skills, mostly centered on getting close enough to the bird to fill the frame. If you want to also look at birds, you carry binoculars and use them when you get close enough (because you certainly are NOT carrying both a spotting scope and a long lens, and you are not getting very satisfying looks at birds through your long lens). With experience and skill your images of birds will be beyond satisfying...they will be stunningly detailed studies of the living creature. That's bird photography.
There are three reasons a photographer might buy a spotting scope and small camera instead of a lens, if he or she is willing to accept the level of image quality possible with digiscoping. Working from a distance, image quality with digiscoping will be as good as and generally considerably better than a long lens working much beyond frame filling distance (arguably, but that is my experience), but it will never equal the quality of a frame filling bird taken at 12 feet with 600mm lens, or even at 24 feet with a 2X extender. The three reasons: 1) indeed, to work from greater distances than a long lens allows, 2) to limit the weight and bulk of the equipment carried (a scope and camera is always going to be lighter and easier to carry than a long lens), and 3) to control expense (Even the best digiscoping rig will cost half what a 600mm IS lens does).
There are no reasons why a birder would buy long lens instead of a spotting scope. :)
Where you see yourself and your desires and needs in all that will answer your question.