How was it, all alone in the aeroplane. (She is not the only one on the plane. She is by herself with other passengers.) I think it’s better to say: “How did you manage on the plane by yourself?â€
Is it cosy with Cathy and her husband? (cosy is an american expression and usually it involves a place like ‘cosy corner’) Isn’t it better to say : “Are you having a good time with Cathy and her husband?â€
And have you already spent all your dollars?
Regards, Willy. (‘regards’ is rather official and this message looks more like a message to a family member) I would just say : “Bye, Willy or So long, Willyâ€
To put things in perspective : my first translation of this text wasn’t correct either!