An affordable intermediate line. If you only want one fly line, then this is it... You can use it for dry flies and as a slow sinking line. You can create a full sinking line with a sinking leader or use a heavier fly.
Regarding backing line... We personally use old mono to save money (or braid)
Re leaders. If you want to make your own 12 to 8 then 4lb fluro is great, or we do have specific leaders