It sounds like you're unsure of the provenance of this footage. Was the film -- presumably shot at 24fps -- telecined at the PAL frame rate of 25fps, which is the easier way to do it?
Do you see any repeated frames in the footage? If so, is there a pattern to it, e.g. it happens every X number of frames?
If you're already satisfied that that the frame rates are correct, let's move to the stabilization issue.
I recommend using your video editing application to export INDIVIDUAL SHOTS ONLY for use in AE. It's then much easier to address individual stabilization issues such as film drifting in the gate, bad camera moves, etc. AE's Warp Stabilizer does a good job of this. Then prerender the clips, reimport and do the slo-mo, image processing and roto work.
Former Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA