Congrats! I hope to be able to afford a second one someday, just in case, but I doubt I'll ever need it!
As dingo said, the easiest way it take the resistance of the carto and add 2. 1.7 ohms, you add 2 and get 3.7v. 3 ohms add 2 and you get 5v. This will get you very close, then you can adjust up or down from there. This is the simplest way to keep it around 8watts, where most people like to
vape.