Good questions. First, I want to ask you something. How do you know what your genetic limit is? The only way you will know what it is, is to get there. Most people will never reach their genetic limit
But anyway, that was just a side thought. You can hold a lot of muscle naturally. The key is going to be maintaining a diet that will support the added muscle. That being said, the quality of your physique won't be as awesome. Gear will give you a fuller rounder qulaity...basically more "pop". Still, you can look pretty good.
Thing is, I've never known a serious guy that has done a couple cycles and then quit using. Steroids are not addictive but GAINS are. It's hard to go back to slow progress