Hi!
I can only speak by myself, but what i use is:
- Activation: the standard (middle one). You can't act offensively unless activated, but can move albeit slowly. I have to try the hard one someday to see if i'm grognard enough!
- Commitment delay rules: i use the second shortest one (i think is the default).
Its not too frustrating (just a little :niark

and gives faily common realist "shit can happen" results where some of your corps on a region don't arrive in time for a battle ad leave the others to fight by themselves. No plan is perfect!
If you want more control, and to know always who is going to fight use the no commitment delay at all.
- Reagroup armies: yes i always tick these on all AGEOD games. Things look tidier and clearer that way to me.
Of course this is only a visual thing. Different stacks don't get merged, they just show as one stack on map, but you can have several tabs per region.
Regards