if you already have the flexTrim, that is pretty much the solution.
seeing what you have would help a lot.
in my experience, coming back after it is all done to trim out doors
is a Royal Pain as the baseboards, chair rails, and wainscotting
have to be removed and retrofitted.
in your CAD drawing, that is exactly what you show.
do you want to do all your arch doors this way ??
if this is your "Plan A" - what is your "Plan B" ?
if you look closely at your CAD drawing, some sacrifices
must be made to achieve the look you want.
again, seeing photos of the trim you intend to use will help.
and your realistic vision of the vertical trimwork.