right then, this could be a long one
-i have used cartography shop to create basic bsp levels, using the .x exporter and bsptox converter included with dbp
-i'd imagine valve offers more than cart shop for bsp's but i've never used it, just bear in mind that cart shop wasn't really designed for .bsp's
-you could definitely use the .x models from 3ds, remember to put your whole level into a box, literally a 3d box, or else you'll get errors.
-a lightmap is created in cart shop(or other progs) after calculating where light would fall in relation to the posistion and properties of light entities.
thats a simple .x map made in cart shop with a lightmap
thats the same one without.
-i could never get lightmapped bsp's to work very well in dbp
-texture baking has something to do with lightmapping, i think its how they make the lightmaps.
-creating levels with a matrix editor+using meshes is fine, also the easiest
however bear in mind that matrices can lower the frame rate of your game considerably so try to avoid using them in large amounts.
checkout out this prog
http://darkbasicpro.thegamecreators.com/?m=forum_view&t=20985&b=5
(download link is further down that page, not at the top)
it uses a matrix to create a completely random city
to cap it off, .bsp isn't really the best level format for db at the moment so maybe leave it, in upgrade 6 it will introduce some impressive features that make .x meshes much better to use aswell, and they are already the best choice imo.
ReD_eYe