1

F8 seeks both videos to the synchronisation point
F9 synchronize one video against the other, in relation to the synchronisation point

To manually fine synchronize, it's helpful to superimpose videos.
May be F7 or F10 could be associated with this feature (not customisable in version 0.8.21)

2

Good idea.
There seem to be some bugs related to hot keys and dual screen though.