Ignatius

Ask her what you can do to prepare before officially starting your first semester. For instance, is there a lab manual you can read/study? (If you are in Humanities, this might not necessarily apply). What books/papers does she recommend? Maybe also send her a shared document where you have some ideas/research topics on what you'd want to study and pursue during grad school. True appreciation comes with a sign of sweat showing that you're actually putting in the work.

I'm unsure how many Engineering Ph.D. programs seriously look into GRE scores of potential candidates, but just to be safe, I'd retake the GRE if you think it's mediocre. I wouldn't take that much time to prepare for it if your comprehension and writing skills are good enough.

https://mpfi.org/training/postbacs/

I've been in a sub-par lab where the PI was uncommunicative and the school environment was dead. I was glad that I was only there for three months. I thought about staying there longer for a Ph.D., but knew that I'd do nothing productive or genuine in such a lab. Doing science should be fun and it it's not fun on most of the days, get the heck out. Daily unnecessary stress is poisonous and is dangerous to the creative mind. From what you've written, I'd seriously consider joining a younger professor's lab with interests that align with yours. Don't think about "causing problems" too much as long as you think it's feasible and the professor is open enough. Science is a hussle and you sometimes have to create your own ruckus before you get squashed.

I recommend starting to see a therapist/counselor regularly. Getting into a Ph.D. program in CS is hard and not getting into one doesn't reflect the value of your life. There might be a silver lining to your situation.

Can I ask you if you've researched out to potential professors/researchers you want to work with? It might be better to talk to them through virtual meetings etc to get better answers that suit your interests and background. Pick out some of the recent journal papers you've read in topics you'd like to pursue and contact some of the authors there. Generally, I'd say 12 months of volunteering + RA would be okay, but the amount of time you spend in research is only one the factors in your application. For instance, by the time you're applying to different programs, would you have made good and worthwhile contributions to the lab(s) you've been in? Would you have built up a good relationship with your PI who can write a good recommendation letter for you? Do you know enough about the work of potential advisors you'd be apply to work with, etc? I can't speak about the opportunities in general terms. This would be another topic to talk with some of your labmates or PI. For the most part, private industry does not invest heavily in basic science.

Ph.D. student in Biology-Neuroscience Concentration here. First, if you are interested in applying to Neuroscience graduate programs, it's good that you have a solid technical background with a degree in chemical engineering. Scientists in biology/neuroscience highly value technical skills and aptitude, especially when quantitative and analytical methods are critical in lab work nowadays. Potential principal investigators would deem your background favorable. Second, I wonder if you have any experience in neuroscience research, or am planning to either start an internship or a research assistant position in a neuroscience lab. I think it's common knowledge that before entering a Ph.D. program in a specific field, it's important to gain some hands-on experience in the field. (M.S. would be generally slightly different because their selection is not as competitive as Ph.D.). Also, I think it'd be good to have at least one recommendation letter from a neuroscientist who can attest to your abilities and potential as a researcher. So, in conclusion, it seems like it'd be good for you to apply to work in a neuroscience lab first and gain some hands-on experience before applying for Ph.D. programs. If you'd be interested in start applying later this year, it'd be good to start working in a lab pretty soon so that you can at least gain several months worth of experience. I'd say that in your case, applying next year or so might be more realistic. Also, I'll say that taking online classes might help but would not be sufficient in building up a strong application. I also recommend emailing professors/researchers whose reearch interests align with yours and asking them for a video conference call to talk about your future plans, what sorts of graduate students they are looking for, etc. It'd be also good to ask whether they are looking for a research assistant, lab manager, or a lab technician in their labs, so that you can possibly fill a role.