For availability, rates or any question about the apartment, email is the way. Expect a reply within a day or two, allowing for the time difference if you are writing from outside Europe.
Worth mentioning in a first message: your dates, how many of you there are, and whether the four flights of stairs are a problem. That last one saves everybody time.
Questions we are happy to answer before you book: whether the bed will suit you, what the street noise is like in your particular week, whether you need a car for what you are planning, and what the weather usually does at that time of year.
Minimum stay is three nights, longer in July and August. The apartment sleeps two and that number is firm rather than a starting position.