OK, you're going to have problems with Cubase. It's good for music creation but not designed for audio post. Nuendo is designed for audio post and provides the functionality you will need for audio post, even more so if you are looking to eventually charge for audio post work. The plus side with Nuendo is that it's extremely similar to Cubase and switching over won't be too painful. The down side is that the industry is very much dominated by ProTools, some producers and production companies won't even consider employing you if you're not using ProTools and as you move up the ladder into decent rates of professional pay, there's almost no escaping the requirement to be using ProTools, to fit in with the all the usual audio post workflows.
As you're just starting out in audio post, now would probably be the best time to switch from a music software package to an audio post software package.
G