I'd recommend trying to use our existing textures whenever possible, adding AO where necessary.
Also, keep in mind that models are not as flexible as worldspawn geometry, so focus on the parts where models would be useful. Flat parts like the ceiling, for example, could be created more quickly with brushes and the mapper wouldn't have to worry about lining anything up.
Where do I find the textures? And what do you mean by "could be created more quickly with brushes"?