The amount will be based on your calculation and the total amount of you income so you will split all of your income in the right allocation.
Besides that, you will not have to use the emergency fund if you are not in the urgent situation that need money. You can keep your emergency fund in the right place while you can focus with your investment.
Part of your discretionary income is what you are to use in build your emergency funds and invest in bitcoin. If you allocate money from your income that's not your discretionary income to build your emergency funds, you will end up using your emergency funds to take care of your needs and any long term bitcoin investor without an emergency funds is only gambling.
That will not be a good way for start the Bitcoin investment because every time we buy Bitcoin will be end up to be used for our emergency needs. We will not accumulating more Bitcoin but it will just stay for a while in our wallet and then we use that amount to fill our urgent needs. Besides that, we don't know how many times our urgent needs come to us so we will not have a chance to accumulating more Bitcoin. That is why we must allocation our money with right to prevent the bad thing happen. We can search for the right info how to manage the income, all income we get so that will works good to our life.