What you seem to be proposing isn't really to be recommended.
The best solution to this problem would be to get into the void above the ceiling and install a proper junction box in place of the existing ceiling rose. Then all you need is to connect from that box to your new light fitting.
You should certainly run an earth wire to the new light fitting, and if it is a type with a metal back plate, then it should have a terminal for the earth wire which connects to that metalwork.
IEE Wiring Regs. have required an earth terminal at all lighting points since 1966.
