I'm new to Android myself. So if someone with more knowlege than I has a better suggestion, please feel free to correct me.
You do not need to do anything prior to installing Go Launcher - except perhaps install "Home Switcher for Froyo". It will allow you to easily switch back & forth between Go Launcher and the standard Touch Wiz home screen. After you have experimented with Go Launcher and decided if you want to keep it, you can worry about removing apps, widgets, etc.
If you decide to keep Go Launcher as your default home screen, switch back to TW and remove all the icons and widgets from the home screens. You do not actually uninstall or delete anything. All the programs will still be accessible in the app drawer. You can also remove all but one of the (now blank) extra home screens and choose Go Launcher as the default home screen.
The reason you do this is any apps or widgets left on your old home screen will continue to run in the background eating up ram and battery power. I found that Go Launcher seems to use less ram, has more customizations, feels simpler to use, and just runs a little better than the stock TW home screen.
If you decide to keep the TW home screen, you can uninstall Go Launcher. Go Launcher does not have that much of a learning curve. It works very similarly to TW. If you already know how to move around your phone, you should be able to use Go Launcher without much trouble.
Regardless of which launcher you keep, the weather clock I recommend is Beautiful Widgets. It will even tell you the expected high temp for the day which the included Weatherbug widget does not do.
Hope this helps.