Actually, a steady income is a MUST for saving a part of your salary in Bitcoin, especially if you employ a DCA sort of strategy. Because it doesn't matter what you call "prepared", if you don't have a steady income then you definitely ARE NOT ready.
U are right , before going into Bitcoin investment it is important one have a source of income , I have recognized the importance of steady income with my own investment journey , it is also good for long term investment success, when their is a stable financial income either with your job or other investment you can manage risk and it enable one be consistent in their investment.
It is not necessary to have a job that gives you salary which you can now remove part from it before you can start investing in Bitcoin, understand what Jjg is saying that
Many of us would like to replace our job with the passive income from our investment, and there is nothing wrong with that as long as we make sure to allow our investment to grow to a high enough level that it can sustain us (and sustain itself).
You don't have to have cashflow from the business or the investment in order for it to serve as a sufficient and/or adequate investment that will be able to support you sustainably and/or perpetually.
Bitcoin can be as good as those other investments that you mentioned, and probably even better, yet part of the secret remains figuring out a balance and a way of valuating your bitcoin in order to be able to live off of its value appreciation and not to overly deplete its principle.