A 6-9 ft leader will work well for most bass fishing. The butt section of most leaders is usually 20-30 lb test which is exactly what you need. The tippet should be a 0-2X size. I like to use tapered leaders and then tie on tippet to the end. If the water is clear, go towards the 9 ft end, otherwise, stick to a 6 ft leader. I also like to use flourocarbon since it's invisible under water.
If you go with the tapered leader, get one that's 9 ft and tie on flies right to the leader until it's 2-3 ft shorter than when you bought it, then add back 2-3 ft of tippet.
My passion for catching fish is eclipsed only by the fish's passion not to be caught.