Hi,
have any of you already installed an openwrt-image on this switch TL-SG2008 what are the experiences?
There is no OpenWrt image for this device, not in 18.06.1, nor in 17.01.5, nor in snapshots.
It's a pity that this is not possible, the openwrt-images can install a lot more than the hardware manufacturers.
It's very unlikely that switches like that can ever be supported in OpenWrt (even before looking at the driver situation), in most cases the CPU/ flash/ RAM aren't powerful enough to even run a modern linux, let aside doing anything useful (like routing or any other service - the vendor only uses them to initialize the hardware switch fabric and to run some very, very basic configuration interface - they often use truly ancient/ low-end SoCs for that, their power lies in the switching fabric, not the CPU SoC).