@Thành0 The long climb upstairs will put off some prospective guests, but it's OK to list the place on Airbnb as long as you're very explicit about this drawback in your listing. If that high-up positioning offers guests a great view, it might even be an advantage.
But whether you can get a return on your renovation investment with Airbnb really depends on how much demand there is for your location. Realistically, your target guests are going to be young travelers on a tight budget, so you'd have to price well below hotels or similar homes with elevator access. A luxury renovation would be wasted here, as 5 flights of stairs is a deal-breaker for most people who can afford high-end accommodation. Another thing to consider is local regulations: even if your city's laws don't currently restrict short-term rentals, it's very possible that restrictions are on the way soon because Airbnb is absolutely radioactive in urban politics.
If the renovation is within your means, and you have a plan B if Airbnb doesn't work out, I'd say go for it! But I'd never recommend putting all your eggs in one basket, especially a basket as unreliable as Airbnb.
