Size of needle varies depending on the situation, however you can refer to below suggestions for choosing needles for metallic threads. It is in the case of one strand threaded (not half hitched)
For all #1 metallic thread including gold and silver, we suggest you to use Handmade Needle - F8.
For all #2 metallic thread including gold and silver, we suggest you to use Handmade Needle - F9
The metallic thread that are thicker than #3, we wind the thread to koma (spool) and couch down with gold or orange couching thread using Machine-made Needle - M3. Hence we do not thread the metallic thread to needle.
You can certainly try threading, however it is not our recommendation as the metallic thread will break while stitching.
If you wish to know the detail about couching technique, please refer to the textbook: