Succeeding in a part time business is possible, but in the initial stages some businesses will demand almost what a full time will demand if not more. I would see it as a part time, but drive it as a full time, if possible.

If you break your day up into:

8 hours to work for your boss
8 hours to work for you
8 hours to sleep

Then if your hours to work for yourself also includes family time, spouse time, house time, etc, then it helps to be open minded to the fact that your sleep hours may decrease a little, possibly until things pick up.

Another thing to keep in mind is, the more expensive your product is, the less volume of people you may have purchasing. Yes it may be more profitable per deal, but if that profit is not sustainable, then you may want to think of a line of products that may always bring you some revenue, while you're waiting for the big fish. Just my humble opinion.