In MC7, you place the cursor where you want a split to occur, right-click, select Split.
Then drag the clip after the split to anther audio track and do the same for each scene.
Yes, more effects means more processor usage, but if you have a modern computer (what are it's specs?) it shouldn't be a problem. If it is, you can then select the track, Process>Apply Effect which will remove the effect from processing and permanently render that effect to the track.
I would make a copy of the uneffected project before doing any destructive editing.