You're looking in the wrong place. The answer to whether you should start a startup or not is not found in the business plan -- it is in you.
I think my issue is that I have a really good job, and the prospect of bootstrapping a startup and potentially not bringing in enough money is hard to accept.
If you start a startup you will have anxiety and you will have long periods with tonnes of work and very little or no income. Do not launch a startup on the basis of a temporary or weak motivation. Launch a startup if you feel strongly drawn to it, even knowing that it will be damn hard.
Sometimes understanding ones own feelings can actually be really difficult. Here are two filters that can sometimes help clarify feelings:
Imagine yourself lying on your death bed. Make it vivid, think of the people around you, and your accomplishments in life. Ask yourself: "If I didn't launch a startup, will I deeply regret this later on?"
Over a period of time, keep a diary of the instances where you think of launching a startup. For each instance, ask yourself a) how did it make me feel, did it elevate my mood or not? and b) what went before thinking of a startup, did I fx have a really bad day at work? Do this over a longer period then review it, and you should see a pattern emerging.
( There is one special exception worth mentioning. Some people are themselves strongly drawn to doing a startup, but hold back due to family obligations -- thinking of the spouse and kids. This case is difficult, and it's hard to give good advice here. One possible way to proceed is to a) discuss the matter deeply with the spouse, and b) try building a business very gradually working in the evenings and weekends, while keeping your day job, and seeing how it feels. )