Does my kWh price have to be the same as my supplier's?

No, you don't have to: you set the price for your guest yourself, separately from your own cost price per kWh. Setting them equal is cost-covering but yields no margin; setting it slightly higher compensates for the risk of peaks and administration. Setting it lower can be smart as a lure during quiet periods, and with a charging station you often charge a higher price because of the greater consumption. What the best figure is depends on your own costs and position in the market.