Thank you Lefty 
I have buyed only the MEGA2560 + touchscreen + adapter shield (that you can see in the first post) for now. For less than 50$ shipping included, I think I made a good deal so I lose nothing anyway, in case I can't get touchscreen + sensors + real time clock all together due to lack of pins.
I have another question about power supply, but I will ask in the french section.