I wanted to try a new Litestep. But download page sais that I need to set up the themes and plugins manualy. Can I expect new installer coming out soon? What happens if I overwrite my previous installation with the files from the 0.2.4.7 build?

The binaries are not a full distro installation, just the executables and required DLLs. You can just overwrite your current files (start task manager, close LS, overwrite, fire up LS).