No strings attached means exactly what it says: you meet, you enjoy each other's company, and neither of you owes the other anything afterwards. No promises about tomorrow, no expectation of daily messages, no obligation to introduce anyone to anyone. It suits people who are busy, recently out of a relationship, or simply not looking for one.
The phrase only works if you both mean it. Say clearly that you are not looking for a relationship, and take them at their word when they say the same. Mixed signals cause the vast majority of the hurt in this kind of arrangement, and they are avoidable.
If you are not sure you can keep emotions out of it, that is a good reason to be careful rather than a reason to hide it.
Decide what you are comfortable with before you meet: how often, how much contact in between, whether you are seeing other people, and how you will let each other know when you want to stop. You are not being cold by setting these. You are being clear, which is kinder than leaving them for the other person to guess.
A no-strings arrangement ends the moment one of you says so. Thank them, wish them well, and do not ask them to justify it. Being easy to leave is what makes you worth meeting in the first place.
Not necessarily. A one-night stand is a single meeting. No strings attached describes the lack of commitment, and it can involve seeing the same person several times.
Tell them honestly. They may feel the same, or they may step back, but either result is better than pretending.
No. A good no-strings partner does not expect constant contact.