Ask your sound post people how they want it broken up. Personally I prefer chunks not a bunch of tracks.
FCP ignores In/Out markers when making OMFs do I recommend you duplicate sequence, delete the second half and make an OMF. Don’t save at this stage. After the OMF is made hit undo and then delete the first half. Make the second OMF and then exit without saving.
By doing it track by track, many systems import the next OMF and default the tracks to tracks 1&2, overwriting or overlaying existing material. Also by doing it in segments, the tracklay can start on the first half of the program whilst waiting for the second half to arrive via ftp for example.