In theory a ceiling rose should take a load of 5 kg. So you just unplug the ceiling rose
and wire in the chandelier and plug back in. However in the main we don't have plug in ceiling roses and often they will not support 5 kg. My arms are weak and holding a chandelier up while wiring it is not my idea of fun, so for me step one is plug in ceiling rose.
Read the thread above regarding your three cables.
One of the cables is the switch drop, the other two form the lighting ring. So no, you dont just join all the wires up. You need to identify the switch drop, hopefully it has red/brown tape on the black/blue wire.