Welcome to your new obsession. Make a six gallon batch next. This will give you a little extra for filling up the carboy (topping off). Try a cider or welchs batch next. Get yeast, nutrient and energizer from your brew store. Be careful with straight citrus, learn the basics first. Take notes with dates and other specifics. Have fun. Be sanitary. Have fun. Buy another carboy. Have fun and be sanitary. There's a wealth of information and experience out there and a lot of it within this community. When you make good brew, it is very, very rewarding. When you get to share with others and they are as impressed as you obviously were, it is truly gratifying. But, it's better than most hobbies, because you get to taylor your booze to your liking. Did I mention sanitation? Have fun!
Currently brewing: Rhino Farts
In Stasis: Rocket fuel