First try using Apolla Orb

I always use manual with OCF. I have experimented with ETTL a few times, but I find the exposure is more consistent with manual power setup. With ETTL the exposure can vary with color of clothing or the pose. Those kinds of problems can be correct with FEC or by adjusting the exposure in PP.

I have a flash light meter that I use to setup my lights. You can use your camera as a light meter by taking test shots and looking at the histograms. An inexpensive white, grey, black card can also be helpful for this. A tight frame of the card will give you a nice 3 peaked histogram that you can center. Also the grey is good for WB in LR.

The usual rule of thumb is 1 to 2 times the size of the modifier. I usually position mine 4 to 6 feet.