Interesting question T&P. Got my first two jobs coming up shortly. Not as large an area as yours but lots of cuts - kitchen with 16 sockets etc and a cloakroom walls with border, where sink/toilet/rad can't be removed because previous tiler grouted 'em in when he tiled the floor! I have allowed myself a week for each job but I didn't tell the customer how long it would take. They never asked either funnily enough.
Didn't want to put too much pressure on myself, tough enough facing your first customer as it is!
Good luck, let us know how you get on