Rewiring European Chandelier
The 18-gauge wire for the arms is fine. You could even go a bit smaller safely if you wanted. The code, Table 400.5 (A) &amp; (B) says that the 18-guage can also handle the entire fixture, although I would like to see 16-guage for the entire fixture. 

I would definitely use fixture wire, SVT &amp; SJT would be good.      

I would use a pre-insulated crimp connector. Use the smallest one that will handle all the wires.  Get and use the right tool.

Spice once only for each lead.