I would like to customize interface but out of the box Gnome doesnt allow me to move panel even. So I want to install xfce but I cannot find such metapackage/template in repos.
Well this is actually tricky question. You want to install something that is not in the official repository but you still watn to get full support for your SLED.
It appears in the official repositories you can not install xfce.
The official documentation - Deployment guide recommends using packagehub as the source for SLED. You still will get support your paid support if using these. However, Xfce is not there either. I would recommend going with KDE 4/5 or whatever you can find there as it has been tested for use with SLED. You can ask there if xfce can be added.
You can also search for your wished package via Find package for any supported SuSE but for SLED 12SP3 you can find only these:
xfce4-dev-tools
xfce4-splash-branding-openSUSE
If you insist on using Xfce as your gui in SLED you have to build it yourself.
I recommend using Administration guide from SuSE
6.2.6 Compiling RPM Packages with build
In general you will be creating a defined build environment for wished xfce. I don't know if it is worth it for you.