It seems that a lot of people who do a research track residency dont end up becoming assistant professors from looking at multiple alumni websites. Many seem to leave research (which is understandable), become forever-fellows, or become clinical/adjunct/adjunct of adjunct of assistant of adjunct professors. On the other hand, there are a few stars who seem to become normal assistant professors very early. Hence the question...
If you wanted to become a research track assistant professor/win a k-award right after residency (so no fellowship), are there any insider ways to do this? For example, defining a clinically applicable research direction early on, going into a new field, doing less basic and more translational work, applying for many fellowships all the time?
You are not thinking about this the right way. If one wants to be a clinician, there's no advantage to become an assistant professor, and an adjunct professor position with more time to make $$ as a clinician or developing administrative experience is much more important. If you want to be a researcher, being a fellow is actually not a bad idea because it delays your tenure clock.
You can go on the market at any time for a basic science job in academia--just provide a CV that is comparable to other candidates' on the market. If you have that CV, a lot of funding will be accessible to you (i.e. K99, NIH early independence, VA, large foundation grants etc.. But the minute you hit that job, your tenure clock starts, and you need an R01 soonish. The entire advantage of a K level award is that you have 4-5 more years to apply for an R01 while you work as a AP/superpostdoc, with a MD level salary. In the medical center system, being continuously funded by grants is basically all that is necessary to get "tenured", which simply means that in case your grant doesn't come through, they'll make every effort to create a clinical position for you, which may or may not be desirable at that point.
I encourage you to think about your life after MD/PhD not in terms of advancing to specific academic ranks but as cycles of pitching ideas to get funding and getting funding to do research and publishing the research. This is because currently the medical center system does not usually have hard money research faculty jobs, except for very rare endowed positions. The academic rank system puts an additional time constraint to getting funding, but ultimately it's always about the funding. Think in terms of when do I get a K, when do I get my first R, when do I get my second R, when do I get my first R renewed etc.
Now looking back the only thing I see that makes becoming an assistant professor "early" attractive is the salary level, which is usually 30-40k more than a fellow (at least). But that's a separate issue.
I realized that it would be nice to be in a job sort of like a humanities professor, where you match after PhD to a tenure track position, then just cruise until tenure review, without having to worry about grants and stuff, and just focus on writing and teaching. But the biomedical research enterprise is just a different beast.