first edit your video in vegas or premiere like you want it on music sounds and so on and then you see what shots you used in final cut so take them to AAE and there do a corrections or FX and render and put these new remade shot instead of the original ones to the final cut on time and render final video its the right way which use every video and FX editor in professional or in some amateur environment
if you want some titles let some space in edit or make there some simple word title to know how long it will be and then do it in AAE and again change the simple one
and if you want cut and rescale all shots to some to some video format do it in vegas or premiere they can do that