Since this plane is powered by an Enya .09, I would not go heavier than .012 diameter. I would start with ~45 ft. lines and if it has sufficient pull, go up to 52 ft. lines. How long the lines should be depends a lot on how well your engine runs, how heavy the plane is and how well it is trimmed.

If you can find a fellow flyer to help you trim it you can save some time and repairs.

Good luck with it.

George