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. If you do it with your fixed income source, it may not be very sustainable. For example,
*Discretionary income is the amount of money left over from your fixed income after deducting all expenses. It is better to invest with discretionary income because you do not need this amount of money very much. The money that is left after meeting all your expenses is discretionary money. If you invest with discretionary income, it becomes much easier for you to maintain it in the long term.
If you do not have an emergency fund, you can create it along with your investments. You can keep some money aside for an emergency fund from the amount of money you wanted to invest from your discretionary income. If you do not have an emergency fund, you can do emergency fund and investment at the same time.
If you invest with fixed income, you may not be able to maintain your investments in the long term. For example, if you need the money, you will have to sell your holdings. So you should invest with discretionary income.
I don't really understand what you mean by fixed income, does that mean all your income (pay) which I don't think anyone can make such mistake of investing with his entire income. Everyone has a bill to pay either personal or extended.
You're right about investing with discretionary income only because that is the best way to achieve a sustainable bitcoin long-term holding but I also want to clarify that you don't invest with all your discretionary income. You only invest a part of the discretionary income and share others into your emergency funds and back up funds. This is a more trusted way of ensuring a long-term holding since no bitcoin stash can make it long without an emergency funds and back up funds.
Having a stable source of income is paramount in setting up your DCA approach to bitcoin investment. This is because you analyse your cashflow and set up a good financial management strategy to allocate every bit of the income to your responsibilities until every of your basic responsibilities are met or taken care of. The money left after handling these responsibilities is what you refer to as your discretionary income from where you also set aside the amount that will go into your emergency funds and the ones that will go into the backup funds with which you can compensate for any excesses in your planned responsibilities. At all, the amount left of your Discretionary income is referred to as the investment funds which is what goes into the bitcoin accumulation.
If someone can be succinct in his cashflow management, provided he has a source of income, the wouldn't be much possible reasons to sell off his bitcoin prematurely. Disobeying your set cashflow system would also affect your bitcoin investment at anytime.