you have to keep in mind that you can't just write a book during a vacation... unless you're on vacation for months now, if not years :-) so I don't know to what extent you want to write a book... is it just for you or for friends and relatives or do you really want to publish it professionally? You'll have to come up with a plan - but you do, I see… at least thinking of one… :-)
If you don't have any experience with writing, I would also recommend workshops at special publishers for new authors. There you can learn a lot and avoid going in the wrong direction all the time... The professionals can help you in time and save you a lot of work when you think you're done with your book....
What is it about, if you don't mind me asking?