Is ist possible to import multiple textfiles (csv, tsv etc.) as layers in one step or do i have to do it file by file?
You can use the tool ogr2ogr and a little one-liner script to import a bunch of csv files together. It will help if you are trying to automate the process or have large number of files.
If you have QGIS installed, you should already have ogr2ogr. (on windows, open the MSYS terminal ). Otherwise grab FWTools for your platform and try the following.
You'll get your shapefiles in /data/ folder.