Contributions to professional cooperatives?

Hello people, My cousin wants to establish a secondary trade in order to be legally able to carry out repairs to motor vehicles for a fee. My question is now, is he not obliged to hire employees BG? Does he have to comply with the same regulations as also large workshops with several employees like e.g. UVV equipment testing etc. How is this if I am employed on occasion on 450€ basis, then what changes? Hope you can help me MfG