It seems to me that you are asking questions that have been answered various times in this thread, so it might be helpful to read through several of the posts in the past month or two, and if you need to refocus your question based on what you read, then come back with some more specific questions.

I am pretty sure that I had several times attempted to address the essence of the stable versus unstable finances in terms of DCA should be based on discretionary (meaning extra) money that you have available after you account for your various expenses, including your emergency expenses.

A person who has more unstable income and or expenses then has more difficulties DCA'ing , but they are still able to DCA so long as they make sure that they create a sufficient of enough reserve or cushion.  I gave some specific examples  in some recent posts that I made in this thread regarding and so it likely would be good to read back through them, but if there is a range of expenses that you have which might be between $800 to $1k per month, but your income varies between $400 and $2.5k per month with many of the months being around $1,200-$1,400, you likely need to keep at least enough reserves to cover the difference between the bare minimum that might come in and whatever are going to be your expenses, and sure some expenses can be deferred, too. 

Maybe a person in this here example that I just gave should try to keep at least $3,600 in his/her reserves prior to investing.  Since the difference between the minimum amount that s/he might make and the top of the expenses is $1k, so $3,600 would be enough to cover $6months worth of low income and high expenses.  If such person has not sufficiently created an adequate enough cashflow reserve, then DCA investing would be risky.. and maybe if s/he aspires to get to $100 per week investing into bitcoin, but if the reserves are not high enough and they are being buit, maybe such person ONLY invests $10 per week while the reserve is being built to a sufficiently high enough level that would be practical, and maybe the person believes that $1,800 rather than $3,600 is enough of a reserve, and that they are not gambling, and so that is their choice regarding how many chances they believe that they are able to get away with taking while still attempting to be somewhat prudent with their finance and trying to invest into BTC at the same time.