"Why the lights are so ugly"
To put it simple, that's not litten very well at all;
Part of updated game lighting means more contrast, which is a good thing in the right hands.
If you want less contrast, lower your light downward a little further or tweak with the ambient light settings in the lights properties.
Second of all , how can I use wads and how to include them?
Wads are now out of date, materials are the new textures. You cant really use wads in the new hammer. If you want to place new textures in, it requires a little more work than in goldsource. Unless you create textures of your own (you'll need to find tuts on it), hammer automatically imports the texture sets of all of the main valve games that you own.
Goldsource Prefabs
Worthless.. You could transfer the brushwork over, but you wont have the textures. That makes most prefabs worthless :/
What's the equivalent of trigger_auto in source ? I can't find it :/
There's not an exact one, but a nice way to cheat it I guess is to place a trigger_once brush over the info_player_start of your map with the same triggers. Gets the same job done-
Why the "light" entity doesn't have a "parent" field?
The light entity is a static light entity. If you want a light entity that you can parent, use a light_dynamic.
Sorry if any of that came out harsh