would taking a 2yr gap following my int med residency (which i will be starting soon) to work as a hospitalist + research, harm my chances of matching in cards or any competitive fellowship
Hospitalist probably won't help much in getting in, but I know a lot of people who took 1 years as a hospitalist to pay back loans, or because they didn't match until 3rd year of residency.
Research may help a little if you get a cards publication.
You can def. still match after doing research for 2 years, but you have to be careful your clinical skills don't degrade. You need to moonlight or something.