Is it possible set a simple and light windows bar? ...below the dock or in another site (in taskbar)?
About install KDE or other DE
You can install KDE/GNOME on Elementary OS, but this isn't recommended, if you want use GNOME install Ubuntu, if you want use KDE install KUBUNTU etc. Anyway, you can install KDE with this guide, works for Ubuntu and Elementary OS, INSTALL KDE PLASMA 5.2 IN UBUNTU 14.04
You can put the bottom bar in Elementary OS without install other DE, you have to install
Enlightenment, you can look this photo and watch the bottom bar.
Enlightenment. If you don't found option
Enlightenmentuse this commands:
sudo add-apt-repository ppa:enlightenment-git/ppa
sudo apt-get install e20
you can try with tint2 https://apps.ubuntu.com/cat/applications/precise/tint2/ is lightweight and simple