Something that has not been covered yet is the difference between being a certified diver and a pro. When you go professional, including dive master, you now carry liability. You also work in a recreational industry that thousands of people see as a "fun" job. The people that have fun are the ones that are on vacation. The pro's are working their tails off for very little money because there are so many people becoming pro that think it will be fun.
Now this is not to say you can't have fun while working in diving as a career, however it is a lot of work and a lot of responsibility. The majority of operations see people that only dive once to a few times per year, their skills are questionable, and often the lack of skills is dangerous. As a "pro" you need to keep yourself and them safe. When accidents do happen, which they will, then come the lawyers.
I no longer am a pro however I have been in the diving industry for a long time both part and full time. Like any other industry there is good and bad. Like any recreational industry there are a lot of people that are trying to make a living, with the high supply there is no ability to demand good pay. I presently have a small niche company that combines all of my engineering and corporate experience with my diving experience. It is still a lot of work and if I were in it for the money I would go back to the corporate world. Then I could take my vacations and let the "pro's" cater to me. It is a passion and for you, at this stage, it is impossible to know if diving is your passion yet.
My advice is, if you are young, get training and/or an education in something that will give you a solid long term career. If you are already in a career keep working to move up the ladder. Take up diving and try it on the fun side first. Then if you want to go "pro" come back to this thread and follow the advice that has already been given, most likely from those with direct experience.
Good luck,