I am an A&P with Inspection Authorization and Rotax "Heavy" training, I would suggest that you first download the free 900 series of manuals. These are free. After reviewing if you still are interested then you can have them printed.
The manuals will provide you with the information you need to know in order to see the differences between the other engine manufacturers and the Rotax engine.
You will also see what Rotax specific tools are going to be required to maintain the engines.
If you expect to make any money you will have to understand the potential costs vrs. what you expect to charge and if there are any customers in your area.
Although I have taken the training up to "Heavy", I generally only work on my own airplane/engine. I make exceptions only when the owners are in a warranty bind. I have provided specific training to an A&P for gearbox removal, and replacing parts in a warranty service bulletin. There have been times when owners contact me from time to time, but usually for oil changes or engine inspections.
I am retired and do not rely on my aviation addiction for income.
My experience is that I would be many thousand dollars in the red if I calculated the amount of money I could make vrs. the cost of specialized equipment plus training.
Many owners do their own work and only call for assistance when they run into a problem. I received a call from an owner who said he had taken his engine apart several years ago and recently decided to get it flying again. He said he was good at taking things apart but not so good at putting it back together again. He wanted me to look his engine over and make sure all of the "springs and washers" were where they should be. I declined.
I would also suggest that you become familiar with the training requirements for Rotax training. You cannot go from basic to Heavy during the same training period.
Good Luck on whatever you decide.