Hello, thank you for your interest!
First: Yes, I'm planning IR4, IC4 and IC2 in N and TT (H0 would be very expansive and its easier and cheaper to mod Electrotren model) - should be done before Christmas.
Later I will do Oresundtog and Litra SA (4-peice ... maybe 8-piece as well).
About the undercarriage - I can't give you exact advice - I'm rather 3D modeler then train builder (I'm building TT railroad, but my models are bought or slightly modded).
Theoretically, IC3 has Jacobs bogies, so DB Talent/Talent2 could work ... but I don't know if you can fi it in - Denmark trains are always "closing" to the bottom (bottom is narrower then middle space) - that is not typical for trains in other countries.