SomeGreatNotion

I feel like one page single-spaced, two page double-spaced was the norm at my graduate school (they did not publish specific standards). Good luck!

I would definitely include it. You could think about presenting it as a journal club under an activities section. I also think listing it as a social psychology lab and putting yourself as a research assistant is fair game too.

I would also poke around on the Society of Behavioral Medicine (SBM) website. This is an annual conference attended by a lot of the health psychology researchers you would likely be interested in.

Ohio State University has a health psychology track nested in their Clinical Psychology program.

Yeah, I would also imagine that you would be competitive as well. My experience in looking at applications for my lab is that so many people look good on paper, it really does come down to fit. Even then, if there is only one spot, someone who would have been a good fit may get squeezed out. If it helps, I went through three cycles before I got accepted in multiple PhD programs. It is possible just keep working at improving and refining your application

I think it depends on what your experience was and how you are framing it to fit your application.

Yes. You will be highly competitive. As for starting, I find the most attention grabbing lines to be short, declarative sentences that begin describing the event. When I applied, I referenced a children's science magazine that sparked my interest. I started with something like "I loved getting mail when I was a kid". Often, I find people try to make these declarations in long sentences that are too difficult to follow. Hope this helps. If you need more insight you can DM me. I am running a small side business editing PHD and internship applications for psychology students.