Thanks Karbo and sorry for the delayed follow up.
Your proposed workaround with temporary rendering a low res version is rather difficult at this point for various reasons (e.g. there are like 20 of the original video files already imported in the project and tagged with comments which I would loose then etc.)
Anyway, since my problem is actually only RAM usage I tried to resort to setting items temporarily offline but ran into another issue (see licecap):
Setting videos items offline 'normally' doesn't work here for some reason (why?). Forcing setting video items offline (action: 'Item: Force media offline') does work (and does reduce RAM usage considerably) but I'm stumped how to set them online again? Normal 'set online' doesn't seem to work and there's no 'force set online' (I can see).
Any idea?
edit:
Nevermind, solved.
'Preferences > Media > Allow videos to go offline' must be enabled.
