BESSY plans to construct a FEL multi user facility for the Soft-X-Ray spectral range from 20eV to 1keV. Central part of the project is a superconducting linac, based on the TESLA technology but operating in CW mode. A photo injector and a bunch compression scheme is introduced, allowing to reach the required electron beam parameters at the undulators beginning: up to 4kA peak current (1nC bunch charge), 1.5πmmmrad normalized transverse emittance and an energy spread below 1%. Extensive Start to End (S2E) simulations have been performed, using the programs ASTRA for the injector part, ELEGANT for the linac and bunch compression studies and GENESIS for the FEL process. Results of these simulations are presented and discussed.