Maarten,

Carsten gave you some good book recommendations. If you look for a nice intro you can get read in a weekend, have a look at Urs Tillmans "Creative Large Format", vol. 1, Sinar Edition. For a more extensive, general book, I still like Andreas Feininger "On Photography". The theory you were asking about is fairly simple linear optics, for a first approximation you won't need more than simple geometry. A good start is also this wikipedia article: https://en.wikipedia.org/wiki/Lens_equation

Regarding your lens, 260mm would be a wide angle for 11x14'' and I'm not sure if you want to shoot close-up portraits with a wide angle. The standard lens would be something like 18'' (450mm). That's just the lengths of the diagonal of your 11x14'' sheet. But this would leave you only 150mm bellows draw, which may not be that much for such a long lens.