FCP X is pretty forgiving about format. Here is what I would do.
- Import all the footage into FCP X
- work your way through each clip. Mark I for inpoint; mark O for outpoint. Hit E and the selected piece will be added to the Timeline. If there is more than one good bit in the clip, then hit Option-X to clear the I/O markers and continue through the clip
- Don't fret about size or orientation or good edit at this point, it can be easily refined later. You are simply building a first assembly
- Once finished, duplicate the Project so that you can always go back to it if necessary.
- Work your way through the duplicated timeline deleting & adjusting I/O where necessary.
- When you get to a Portrait orientation scene, adjust the size percentage in the Info window to suit. You will probably reduce it to add black borders. You can try blowing it up and re-positioning the X,Y axes but likely the quality will fall apart.
- You have now created a First Cut
- work on the soundtrack now using either the sound captured on the video or by adding music. If you find you need the sound but not the video, Detach the Audio and adjust it as a separate element. Don't lose synch! Undo is your friend. I always add markers to both video & sound elements to re-establish synch if needed
More than this Kevin, you need to go to Ripple training and get their videos! ))