De-interlace and IVTC are two different things.
De-interlace is used to "convert" fully interlaced video into progressive video. There are various ways to do this. But the idea is usually to merge or blend the fields. You CANNOT IVTC interlaced footage.
IVTC is used to convert telecined footage back into normal it's normal progressive format. You should not have to de-interlace after you're done IVTCing. IVTCing is not really a true form of de-interlacing. Though you could somewhat consider that it is, since it removes "interlacing" that was added due to the telecine process.
Somtimes IVTC does not work completely and you must run a de-interlacer to remove left over field artifacts.
All NTSC(USA) IVTC'd materials got the NTSC 23.976 FILM rate. Premiere doesn't support this, so you could use AssumeFPS(24) if you want. It's not needed. As long as your previews look fine in Premiere you'll be good to go. You don't want to start on the project and then adjust it later. If you want your project comply with NTSC standards then you should read the guides which explain how to do it. Premiere is such a suck ass program it doesn't allow for 23.976 projects.

Baka Premiere
~klinky