One small to med sized shrimp will take care of it. I would go ahead and add the LR
unless you intend to buy already cured rock from a local dealer. If you do intend to add cured rock, just toss the shrimp in and start checking ammonia levels. Add the rock as soon as the tank has cycled and nitrite levels are steady at 0.
If, however, you intend to use rock ordered online, you can use the rock to cycle the tank. You'll have enough die off with this type rock to take care of the cycle.