Hello Victoria
It sounds in a great location - but does it have any issues like being in a noisy location that might impact on lettings.
Have you done your research on BnB to see how many similar properties are available on BnB, what they charge and availability. This will help you understand your competition and how busy they are. What's the market like more generally in terms of self-catering properties to let?
Have you spoken to Visit Edinburgh or tourism body about the self-catering and the marketplace?
If you need guaranteed income you may be better looking at long term lets. A minimum 20 nights X 12 months sounds quite high - but you might be in an area that has a shortage of accommodation and you can charge much more during the fringe, new year etc.
Do your market research. If you decide to try look at how you can drive traffic to your listings through promoting through your social media, friends and family and see whether you can get registered on tourism sites.
Good luck.