If you don't want to read the Gentoo handbook, there's little we can do to help you.
You really need to get your hands dirty to install Gentoo. By the time you read the handbook, and use it as a guide to install your Gentoo OS, almost all the questions you made above will be solved.
- The terminal is the default, since the very moment you start installing Gentoo. In fact, there's no GUI until you install it.
- You don't have to do anything to use multiple desktops. Just install them.
- Same goes for login managers, the one you'll be using is configured by editing /etc/conf.d/xdm. More about that in the X configuration guide, and in the respective desktop howtos.
- Using every DE out there is usually not compatible with the term "lighten". In any case, I really doubt you need that fine grained control. You probably didn't mean "real time" either. That words have a very concrete meaning in computing. If you think you do, please, let us know which concrete tasks do you need real time for so we can help you better.
In addition, you will need this to set up Xorg:
There are also guide for kde, gnome, xfce and some others. One at a time, and you will be successful.