My opinion is that pricing based on what you need to pay the mortgage or recover what you have put into the house is unrealistic. Of course do financial projections to determine a rate for your net profit objective (revenue - expenses - recovery of capital investment, as Jacquo says), but I wouldn’t base my rate on that.
Compare with what the competition are charging to see if your goals fit with market reality. I get that there might not be exact comparable properties, look instead at the choices your target market has in the area. I gather you are in a sea/holiday area, so don’t ignore hotels that may also appeal to your guests.
Of course the nice thing about STR vs LTR, in addition to higher rents, is that you can experiment with pricing.
The price differential between platforms may in part reflect adjustment for the lower service fee charged to hosts by Airbnb (I thought they were going to up to a flat host 15% or something, but hasn’t happened in my locale yet.)
Personally, I would never say my place is “immaculate” in a Airbnb listing. There might be one off day when the place isn’t quite immaculate, or one set of guests who have a ridiculous definition of immaculate (“There were dead leaves on the welcome mat!”). I don’t want to give them ideas for complaints. Underpromise and overdeliver has been advised many times here on the forum.
I agree the realtor (you call 'em estate agents, yes?) type description of the house is maybe too much and taking up your word count. Bullet points are easier to read. Let your photos speak for the “light, clean, modern look” and “cosy, intimate living space” rather than making statements. Those are subjective descriptions that may or may not match your guest’s expectations. You could state some points more briefly as your photo captions. E.g., for outside shot of the place: “Welcome to our mid-19th century workers cottage, updated!” The garden: “Dine al fresco with a garden view.” Etc.
But don’t worry overmuch, as the guests won’t read your listing anyway!
As a former landlord, you probably have thick skin, but I’m also hearing justified pride in your careful and extensive refurbishment. You need to steel yourself for the black marks from luggage bashed into the wall, scratches, spots on the carpeting, and whatever.