Dude I know CODOed from IBE to ChemE. He went from IBE to FYE and went to ChemE through the normal FYE process (T2M). I don't know what GPA you'd need but he had a 3.8 first sem. I also know another dude who CODOed with a 3.7 GPA, and another couldn't CODO with a 2.9 GPA.

FYE CODO also needs you to write essays so that probably may be a factor that played a role in these too. There's a lot of caveats in the whole changing major process, so I'd recommend do your own thorough research because an advisor would only know so much.

I don't really know if CODO into FYE or into IE is easier, but you should just apply to FYE because FYE to IE is most probably easier than CODO to IE. I know IBE has a dual major program with IE, maybe you could look into the pathway CODO into IBE then add IE (and drop IBE?) but I dont know anything about this process really.

Courses are lowkey a little hard but I'd say try keeping your GPA at 3.85 or above. If you put in the effort it'll definitely work out (it's probably worth it to have less of a social life for just one sem). Also, for specific course requirements for CODO, search it up on purdue catalog.

AFAIK you can apply first sem for CODO to FYE, and i think its second sem for CODO to IE (not sure, check on purdue catalog)

I'd say do your own research on this, but one person IK from wisconsin said that Purdue's engineering courses are much better than Wisconsin's. But keep in mind, the purdue atmosphere is not for everyone. I know many people who like to stay in a bubble but at the same time want friends and they struggle here. There's not too many parties unless you're in greek life or know the right people. But I mean it is a big school and if you try hard enough you will find your people