You need a lot of willpower, and you need to be able to take criticism well. Your hobby is no longer something you do only when you want to unwind and relax. It's a business now. Do it or die. Because it's a job, people will give their critiques and you will need to separate yourself from those words and not take them personally.
You will need to be able to handle stress from something that once destressed you. It's a change of mindset, but an important one to make. If you're not passionate about your hobby, and only go in half-heartedly, it will be extremely tough to turn it into a long-term career. It has to be a passion and you have to apply dedication.
You will need to find another hobby to unwind from your job hobby, preferably in a different realm. Like if your job hobby is artistic, do something physical to let off steam. This is critical. I wish someone had told me this before I started.