Keith,
An excellent question. It sounds like one of those question that everyone wanted to ask but was waiting for someone else to ask it. I understand where you are coming from both as a software engineer, as well as being a professional magician (peformer).
I agree with Eddie about different places wanting the entertainment. There is usually a person in those facilities that handles the entertainment. Contact them and see what their schedule is like and when would be a good time to perform there. Most are ususally looking for entertainment throughout the year and have many "volunteer" entertainers around the holiday times.
Try a few places out and see how you like it. Do not go by just one time since you have to match the audience with what you are doing. I found after playing piano at an old age home in NYC once they wanted different music than what I had memorized. I then got more music for that type of performance and the next time was a big hit. You never know.
When I perform for any kind of charity work I explain what my fee is and then explain that I will be giving them a "donation" for the full amount. We then trade checks at that time. This way you are not working for free and you are making a donation to a worthy cause at the same time. The people also have a better feeling for what they are getting. You can do this if you are comfortable with the idea after you get established.
I enjoy performing (whether magic or music) around and tell people that I get invited to parties and paid for it! It is a good feeling. If you see one person singing along you know you did a good job.
Keep us posted on what you do.
- Brian