The server can be hosted in a variety of ways and there is not really a right or wrong answer - just what suits your own needs. But I would suggest a basic setup on a pc while you review and setup your implementation would be the way to go. A hosting environment can always be looked at later on when looking at going into a live environment. There are also cloud hosting services offered by xTuple to consider.
Just to clarify I am both a user of Postbooks (a user for about 3 years in a family industrial business in South West Sydney) but I am also establishing myself in my own business as an xTuple Partner (I like it that much!). I live in Wollongong.
I am more than happy to assist you get started both here on the forums and more substantially at your business as an xTuple partner if you wish.
What business management issues are you looking to address with Postbooks?