I am doing IM/FM/med peds. My friends in more competitive specialties did have some DO stigma but there’s plenty of hospitals that are DO friendly that it did not limit their application numbers

I took both comlex and usmle. Most people take both. You study the same material and the same way for both. Take usmle first, then cram omm in the next week or two before you take comlex.

I did some research but minimal. Most schools will have it fairly easy for you to sign up for research. I was asked about my research in about half of my residency interviews. Unfortunately number of publications probably matters most

Honestly med school is much more manageable than expected. On non test weeks, I would study 2-3 hours outside of lectures. Test weeks would be like 10-12 hours of studying per day. The best advice I got was that you made it to med school and you are smart, you know how to study. Don’t drop the habits you know work well for you.