shooting school formal

I am shooting a formal this Friday, with a mix of full length shots as well as waist high (couples and small groups.)

I have an 80cm soft box, and two umbrellas, one silver one white (both 60cm)

From what I have read is that I should have a main light off to the side, with the female closer to the side and a fill light on camera axis , a bit higher than the camera.
(both are flash based and using wireless remotes)

My thoughts are the soft box as the main and the silver umbrella as a fill, with an approximate ratio of 2:1 (main : fill)

Plan to use two cameras - one crop with 28-135 for full length and the 70-200 on a FF for closer.

Does this sound right
(happy if you point to relevant threads)

If you have enough room, the 70-200 on the 5D will be the only camera you need.
Keep it simple if you can.

Be careful with the group shots that people don't block the main light from one another.