I wouldn't get a reading prescription in riding glasses. I use varifocals normally, but not in the riding glasses.
I wouldn't use the lenses I have (black iridium photochromatic IIRC) at night, but should be ok for overcast etc. I don't do night riding as a general rule though so it wasn't a big consideration. I suppose only time will tell how it works out in the autumn and winter.
Normal transitions would probably be a good idea, I haven't seen those as an option for Oakley, only the tinted photochromatics that start with a slight tint and then get darker, hence the new lense I mentioned somewhere above that I can't find for prescription yet.