If you like to have a hot drink if you wake during the night why not take a Thermos & fill it at the self service or get your steward to fill it with boiling water in the evening. I have done that before with no problem.
You are not allowed to use a travel kettle for health and safety reasons. They don't want a fire on board. There is no need to 'buy a package'. The tea and coffee is free 24 hours a day. Help yourself in the buffet. Coffee served after dinner in restaurant, also free.
No but there is no need to, free tea and coffee is available on the Lido deck and in the Lido Cafe 24/7.