I hope I am able to make some sense, but I notice that
Business owners after some time begin to consider to open up more business outlets for their business, or start up other businesses,
Traders after some time start up a trading academy to teach people and earn more almost like the next phase of growth in trading,
What is the next phase for a successful bitcoin investors ? or what would you advice they do?
I can only use the word "seeing is believing" to make an example out of your question, I know one or two Bitcoin investors that are now very successful and one decided to venture into Bitcoin mining farm while the other opened a big restaurant in his city.
After becoming a successful Bitcoin investors you should never stop accumulating Bitcoin and think out of the box, like use some money to create a new business or startup somewhere, this is all I can say, the rest lies on you shoulder, find something that suits who you are and start from there.
I am a business owner before I started investing in Bitcoin, but I was not making alot of money then, still I decided to learn more about Bitcoin and trading, which in return helped my business too, I have other plans for the future as well.