I can talk a bit about what appeared to allow my daughter to successfully pursue this path (at least up to the point of getting accepted to a PhD program and liking it for the first year plus a bit). Some of this is stuff that you will not need to worry about for several years.
PhD admissions is very competitive. It is a good idea to plan to have an application that is strong in multiple dimensions. Good grades as an undergraduate student will help. Research experience is most likely essential. Fortunately you are already started on getting good research experience. Letters of reference will be important, but is likely something that may result from research experience. It is important to have a good idea what sort of research you are interested in, and why. Having some research experience again can help you decide in more detail what you want to do. Eventually, when it gets time to actually apply to PhD programs, it will be a good idea to understand what research is already going on at each school you are considering, and how that relates to what you want to do. As one example, when my daughter was applying to PhD programs, she had already read the academic papers by professors working in her field at each university she was considering, and could refer to this in her essays. Before interviews she re-read each professor’s academic papers, and went into every interview with at least one question to ask each professor about their specific research.
PhD programs are typically fully funded. The university pays your tuition, fees, and provides health insurance. Also, you typically get a stipend which is enough to live on as long as you live very frugally. One small issue is that PhD’s can take 5 or 6 or 7 years, and it is not really a great idea in the very long run to postpone contributions to retirement funds for this long. Congress has apparently clarified that the academic stipend counts as income for purposes of funding an IRA, but you are not going to be able to afford to do this unless your parents or someone else helps you out financially. Also, the stipend is typically minimal, and some small amount of parent financial support can make the 5 to 7 year marathon easier to put up with. With a small amount of parent support (emphasis on “small”), a PhD can become basically an interesting job that provides you with the opportunity to do interesting research, with the understanding that in the off chance that your research eventually succeeds they are likely to eventually give you a doctorate.
Of course one definition of “research” (that I first heard from an MIT researcher) is: “You might fail”. When you are trying to do something that no one in the history of the world has ever succeeded in doing, success is not guaranteed. Patience is going to be needed. “When” (not “if”) your experiment fails, the ability to figure out what most likely went wrong and fix it next time will be important. You might have already learned part of this from the research that you have already been doing.
I do not understand how someone could pay off undergraduate student loans while also pursuing a PhD. This is just another reason to avoid undergraduate student loans if you can.
To me it looked like applying for a PhD was partly like applying to university, and partly like applying for a job. Similar to a job application, the professors deciding which students to accept might be thinking about whether they want to work with someone for multiple years. My daughter has said that the program that she is in seems to have accepted students with kind, responsible and cooperative personalities. I expect that this will come across both in letters of reference and in interviews.
This is however the right path for some students. Also, a huge percentage of humanity’s long term progress depends upon someone doing research and doing it well.
By the way, if my daughter had not gotten accepted to a PhD program there is a good chance that she would have been accepted to a master’s degree program instead. A master’s typically is not funded. One plus here is that a master’s is typically two years, or for some professional master’s degrees (not research-intensive) maybe only one year or 1 1/2 years.
Of the other students in her PhD program, quite a few have master’s degrees but I am pretty sure that the majority do not. Quite a few had some work experience after getting their bachelor’s degree before applying to PhD programs, but not all did. Some came from famous undergraduate schools (Harvard, a top LAC), but most came from more average universities and some came from colleges or universities that I have never heard of. Some were not from a “top 100” undergraduate program. “All over the place” might be a good description of where they got their bachelor’s degrees.
ECs might be difficult to fully evaluate, and people commenting her on CC might have different opinions. My personal belief is that for ECs you should do what is right for you and do what you want to do, and whatever you do, do it well. To me this is my understanding of the recommendations in the “applying sideways” blog on the MIT admissions web site (which is worth reading if you are applying to any highly ranked school, or even just to read it and see one perspective). This also looks to me to be what you are already doing. Personally I like your ECs. What a university admissions staff will think of them is yet to be seen.