Not everyone gets that far, Ironclad Oz, and some do very well. After 6 months you'll have a good idea of how you're going, after 12 months you've found your level. This level could be 3 clients doing 2x30' a week each, or it could be 30hr a week of sessions, etc.
It'll grow a little bit from there, like 10-20% over the next few years, but unless something drastic happens - you move from Woop Woop to Melbourne Central, you have a training epiphany, whatever - you'll basically find your level in 12 months.
You don't know until you do it. Experienced and successful trainers will be able to meet you and judge it for you, but if you're relying on your own judgment, you'll take 12 months to find out.