As for the stainless, .012 is for high powered .049 competition such as Combat. For sport or stunt flying, .008 x 35' or .008 x 42' is ideal.
These lines, though strong, are very fragile to handling. Monofilament fishing line such as Spiderwire is much easier. Just make sure the knots stay tight by using the correct knot and/or applying glue to the knot.

George