1) Shooting at 50P would help as then it’s just a matter of discarding fields.
2) I don’t think for the 25P to 50i you need Twixtor, FieldsKit Reinterlacer mode Motion Estimated Fields would do.
A. In Premiere you work in a Progressive Sequence
B. You apply FieldsKit Reinterlacer, Upper Field FIrst – Output Create Motion Estimated Fields
C. You export Upper Field 25 FPS
and you should be good
3) Now you need to apply this to individual clips on the timeline, otherwise you will get a weird second field at the end of each clip (as it will look otherwise to the next field which is completely different).
Clear?
Pierre