How should I spend 1–3 gap years to become more competitive for research-heavy MD-PhD programs?

Hi everyone! I’m trying to figure out how to use the next 1–3 years strategically before applying MD-PhD, especially if I want to eventually be competitive for very research-intensive programs.
For some background, I graduated in three years with a BS in Biology and a BA in Chemistry, around a 3.94 GPA, with honors. I’m currently completing a 4+1 master’s program.
Research-wise, I’ve been involved in research for several years, but a lot of my more recent work has become computational/bioinformatics-focused. My master’s thesis is also primarily bioinformatics and is more independent than some of my earlier work. There is a possibility of publication, but I don’t currently have a strong first-author publication record.
I think this is probably my biggest source of uncertainty. I’ve done a decent amount of research, but I don’t feel like I have the kind of clear research productivity/ownership that I see from some successful MD-PhD applicants. When I look at applicant profiles online, I see people with multiple publications, abstracts, posters, conferences, etc., and I honestly don’t know how far away I am from being genuinely competitive.
Clinically, I’ve been doing clinical volunteering consistently and currently have inpatient, patient-facing experience. My bigger weakness is that I have relatively little shadowing so far.
I’ve been debating what to add next clinically. Some possibilities I’ve considered are:
more shadowing
working as an MA or scribe
becoming a clinical research coordinator
continuing my current volunteering and keeping the rest of my time focused on research
I had also considered EMT at one point, but I’m increasingly thinking that the time commitment may not make sense for me.
I’ve gotten mixed advice about this. Some people have told me that for MD-PhD, I should mainly strengthen my research and just make sure I have enough clinical exposure to clearly explain why I want the MD component. Others have said my “clinical story” may still be relatively weak and that I should build more substantial clinical experience.
Outside of that, I’m currently a TA and have teaching experience as well.
My main questions are:
Research: After my master’s, would it make more sense to join a large, highly productive research lab and spend 1–2+ years doing full-time research? How important is being in a very strong lab versus having more independence in a smaller setting?
Research output: Should my main goal be getting stronger primary research publications, ideally first-author? Would writing reviews or other papers meaningfully help, or should I focus almost entirely on original research?
Clinical experience: Given that I already have ongoing clinical volunteering and inpatient patient-facing experience, how much more would I realistically need? Would you prioritize shadowing, CRC, MA/scribe work, or just continue volunteering?
Gap years: From a profile like mine, would you expect 1, 2, or even 3 gap years to make sense if the goal is to become competitive for research-heavy MD-PhD programs?
Conferences: How important are conferences/posters/abstracts for MD-PhD admissions? Should I actively try to attend and present at multiple conferences, or are they mostly secondary to the actual quality of the research?
Overall competitiveness: For people who applied successfully to highly research-intensive MD-PhD programs, what did your profile look like when you applied? How far does someone with my background still have to go before being realistically competitive?
I’m very willing to work hard and take time before applying. My biggest issue is that I’m not sure where the highest-return use of my time is anymore.
I don’t want to spend two years accumulating activities just because they look good on paper if what I actually need is deeper research experience. At the same time, I also don’t want to over-focus on research and realize later that my clinical exposure was too thin.
Would really appreciate advice from current MD-PhD students, applicants, or anyone familiar with admissions.