You can add fog to your map, for your sky add :
"sky" "pbsky4 fogd .5 .5 .6 .002"
".5 .5 .6" is the color of the fog
".002" is the density
To add flag:
Press "e" , choose "Flag"
Press +
Key "teamnumber"
Value "2" for blue flag , "1" for red flag.
You will also notice that you still cant cap the flags thats why you need to make "base"
How to make "base"
Make a brush into the area you want the flags to be capped, press "s" and choose "Mist"
Click on the brush you just made and.. (Read below)
Press "e"
Choose "base"
Press +
Key "teamnumber"
Value "2" for blue "base" and "1" for red "base".
Also I dont know what do you mean by splash?
Hope that helped.