6# Spiderwire is sorta minimal, I'd use 8# anyway, maybe even 10, even for an .020. .049s need 10-12#. Terminate the ends by tying a Palomar knot onto a line connector (fisherman's knot).
Line length: For .020, 27' lines work pretty well. Maybe could go down to 20' but you'll be spinning pretty fast. With .049s, even mild ones, 35' is better.
I've used spiderwire for leadouts, with just loops for attaching the lines, strength is OK but had unexpected difficulty getting line connectors thru those limp loops, especially after a flight or two. Wire leadouts are much better--they hold their loop shapes. either solids ('way thin, maybe .010" or so) or braided--I use .008 7strand very successfully. Kinda fragile for flying lines but work very well in short lengths such as leadouts.
Hope this is helpful.