Enough for being able to match a fellowship if I bust my ass and publish etc?
Sure. Why not.
Here's the problem with what you're heading into.
1) You're going into Internal Medicine aiming for competitive specialty medicine. What happens if you don't get it? Are you going to be miserable doing hospital work - i.e spending a lot of your time consulting others, pain management, electrolyte replacement, managing run of the middle AKI, CHF, COPD AE, A Fib w/RvR? Will you be happy if all ends badly potentially switching gears into a different fellowship?
Like critical care you probably can match. You just might have to do Nephro or ID first as a lot of programs borderline advertise themselves as combined programs for those willing.
But what if you decide by your 3rd year you're too tired for more training?
2) You're switching from Cut Cut Chop Chop Land to Medicine. You're going to spend 2 hours a day literally rounding and trying to elaborate on the intricacy of hyponatremia, volume status, and fluid rates to run to prevent overcorrection. You're going to be on the ground to manage blood sugars for surgery after they're done doing the "important" part. And now just want you to get their patient medically optimized to go to SNF/SAR for recovery.
And honestly, it's not for a lot of people. I will actually say that I enjoy hyponatremia management. But I also enjoy physiology and manipulating bodily chemistry. Will you get extremely exhausted doing this?
Fundamentally this a 3 year residency. It is not a bridge to fellowship. It's a bridge towards being a generalist. You're expected to be good at it. Not good at your one thing you like and screw all the rest.
I'm not doubtful you can pull it off. I just want you to be realistic about what you're going into and not look at this as some sort of COMLEX 3.5 or 4 hoop.