I literally only just discovered "loop segment" scrubbing minutes ago, which is why I documented my findings in this video because otherwise I'll surely forget all about it in a few months. So "Here's how I use Reaper etc etc" should've been "here's how I might use Reaper"; I'm a big liar.
I'm still debating whether I should use Reaper to actually put my animatics together because it's a DAW that can also do basic video editing which appeals to my musical timing sensibilities. Before I'd use awkward metronome sound files in Vegas. Maybe I'll use my usual video editor for getting a rough idea for story etc, and then use Reaper to get the timing perfect using tempo maps, making a rough score as I go, then transcribing the information to dope sheets.
Of course re: frame 0, can always set frame 0 to be 1 frame before the scene starts, which is what I'll be doing for transcribing the visual timing, but that isn't necessary for the audio scrubbing.
Also re: sample rates, Flash MX is really weird in that it'll play sound at the wrong speed unless I set the audio card and .wavs to specific sample rates. It's a real nuisance when doing lip sync, or even judging how long a given scene is.