Launchers are far less invasive then most people [who have never used them before] assume.
When you install a new launcher, it does not delete/replace/remove Touchwiz Launcher...it simply changes the place your phones goes for "Home". When you first install a new launcher and press the Home button, you will get the standard app picker window asking which app to use. You will see Touchwiz and, for example, Nova, both show up there...you can press either one and it will take you to the home page for that launcher and you will not see any trace of the other.
I recommend you keep it like that for the first few hours or days, while you customize the new launcher the way you want. Once you are comfortable, you can then save one as the default and it will go there every time as if it was always your launcher. At any time, you can switch right back to Touchwiz if you want and the new launcher will just be there waiting. If you uninstall, it's like any other app, and it disappears and leaves no trace it was ever there.
It's really very simple and clean and safe...and EVERYONE should try it at least once. My recommendation is definitely Nova, but other launchers are excellent too. The customization options you get are absolutely awesome and powerful.