If you are going to be purchasing tapered leaders you may be able to find a "bass taper" or a "bluegill taper" type leader. Depending on what type of flies you are fishing for the largemouth you may need something fairly "stiff" in order to turn over the large wind resistant poppers etc. So if you are going to tie your own following the earlier posts formula I recommend something like Maxima or Mason for your material. If you cant find a bass taper try a "bonefish taper" which should be plenty long, strong and stiff. Depending on the type of cover you are fishing and the water clarity I think I would start somewhere around a 9' 0X tapered leader. Buy yourself a spool of 0X tippett and add a foot or two of tippett to the end of the leader. This will give you longer leader life and a little more distance from your fly line to fly. Attach with a blood knot or a double surgeons knot. For bluegill I would think a 9' 4X again with an extra foot or two of added 4X tippet would be a good start.
Nice bass by the way!