It can be used. I cannot answer the question about the additional cable because I do not know which cables are already present - the charger does not come with any cables.
I have purchased additional cables that withstand transport particularly well: https://www.digitec.ch/de/s1/product/xtorm-cx011-a-c-1m-30-usb-kabel-5889772.
Yes, that is possible. I use it for iPhone, iPad and Watch for the whole family. Charging time approx. 40 min and the iPad Pro 12.9 is at 85%. Would buy the part again, but then with more than just 2 device ports. GLTA