I don't think that is being overly cautious at all. Youv'e built no rapport with this couple, general communication has not been established...and how do you REALLY know that these people are from Germany or they aren't out to scam you?
This is a true story and I'll tell it best that I can remember it. I say that it is true as this discussion came up with a couple in the group of Northaven couples that we met with once, who are from the Chicago area, who knew this person well. He is very well known in swingers areas there and well liked.
On the ad site that we belong to (when it still had a forum) this sort of discussion came up. Some background first on this persons story. This person is a single black male, upper 30's, primary residence in the U.K. travels between the U.K. and Chicago often on business. He received an e-mail from a white couple that wanted to meet him on his next trip to Chicago. They never offered much info, he didn't really know much about them and it had never been a problem in the past to give out info on where he would be staying, etc. (I'm thinking he had been swinging quite some time...ten years maybe?) They offered for him to come to their home as opposed to meeting at the hotel lounge for drinks, etc. Again, he thought nothing of it.
He was told they lived in a really hard to find area, so they would meet him at some local establishment and would have him follow them from there. Again, thought nothing of it. He met them at the designated time, exchanged some brief hellos and then followed them to 'their' residence. Turns out it wasn't their residence and that wasn't all he was meeting. He was met by a group of men and upon exiting the car they beat him into unconciousness. He then spent three weeks in the hospital before being able to return to the U.K. He recalls very little about the incident other than being called a 'filthy nigger'. These people were eventually tracked down (idiots...like he wouldn't tell them that he had met them thru a swinger site that houses their personal info) arrested...and I don't know the final outcome. Who says racism isn't alive and well in America today?
The point I'm getting at here is while incidents like these are probably rare... It doesn't matter if you are single, a couple, male or female... always err on the side of caution. The web is a powerful tool which can attract the worst of the worst. Always follow your gut instinct and I'd say since you are questioning it, don't give out the info. Your safety comes first.
Now to answer your original question.
We will not give out any personal information...unless I approve it first. (I being the more cautious of the two of us.) This information is never given out until I feel comfortable with whom we have corresponded with. Having spent the majority of my adult life as a single female, it is ingrained in my head to do so.