Ok, lets do this backwards.
Yes, you can make fancy models. You need an external program such as milkshape or that other one I can't remember.
To make writings on the wall you need spraypaint and a gangster person; however, in Hammer, you would use something like wally.
And for your first question....
Mind you this is not my idea I got it from this guy I cant remember so give credit to that guy [whoever the hell he is].
[I was going to post a link to the tutorial, but I cant find it.... I really didnt want to type it all out, and I swear to god if anybody posts the link to that tutorial....]
What you do is you make an entity ambiance_generic
select it hit alt+enter
in the path input type ambiance/*.wav [where * is the name of your music]
under the flags tab check play everywhere
and play on start
Location Location fucking Location
ok you want to make a box outside of your map
place the ambiance in there
repeat [via copy and paste] to all sides [north, south, east, west]
your music will play if and only if the following is true
its a wav file [ie .wav]
its less than three minutes [roughly]
8 bit mono
11025 hz pcm
it is in the directory *\valve\sound\ambiance\ [where * is your counter strike folder]
you can use audacity [free] to cut your music down to size
you can use ease audio converter [trial] to convert it to wav [it has all the options to make it work for cs]
I think I have arthritis now.