get to know how to move around with the camera at first, that is most essential. and learn the shortcuts http://www.dswp.de/old/viewtopic.php?f=6&t=431



SIDENOTE:
you could as well "model the map" with another program and export it to a .map file... http://www.katsbits.com/htm/tutorials/blender_export_model_to_map.htm

can be WAY easier compared to making up everything in the radiant. it is likely tha you will fuck up the scale as any other program is not likely to use units. (blender can do: http://www.katsbits.com/htm/tutorials/doom_3_prepping_models.htm#blender_grid)
i got no knowledge on this topic, wrote this just to mention that there a different possibilities. that may be much easier and worth to take a look at. (i will most certainly after the train remake)

BUILD

A

FUCKING

CAULK

HULL

!

means:
use structural caulk brushes for a very basic layout of your map, and fill it with detail brushes... makes HINTs and the VIS stuff MONSTER-TRUCK-SHITLOADS easier.