Hi Mike
The copper wire a nighmare to get stright. Like Colin said get your self some 1 meter lengths of brass rod. You can get 0.3mm
and bigger sizes.
Use flux my self I prefer decent flux I use plumbing flux. Then I use solder paste. This means you can very easily control how much solder each joint gets.
Then solder them up. Afterwards a wash the hand rails in bole of boiling water a a drop or two of washing up liquid. This will remove flux resadue. If you dont the brass will corride.
Done several 1:100 ferries this way.
John