An emergency fund should be considered essential by anyone considering long-term Bitcoin investment and not wanting to disrupt their Bitcoin balance every time they need cash. However, I recommend everyone have a steady job with a regular income stream so they can manage it carefully, including allocating a portion of their income to an emergency fund and using the rest as capital to buy Bitcoin.
To invest or create an emergency fund, we need a source of discretionary income.
That is a contradiction, you don't need a source of discretion as discretion is a leftover money after your total expenses. Your source of income may be from a job or any work that provides an income, but not discretion. Discretion is just the remains from the income you generated after expenses.
If you do it with your fixed income source, it may not be very sustainable. For example,
There is no one that invest from there fixed income but from their discretion fund.
Well I think you have said all I wanted to say in the last paragraph just that there is a little misconception in the fist paragraph.