This is a fair-sized tree; unless it is curly I will probably take it all at 5/4. If it is curly, I should be able to get 4 planks about 3" thick and 15-18" wide, by the length of the log, which should be 10-12'.
Ash is one of those trees that seem to dry better if you square the beam up before sawing (you want to get rid of the bark and whitewood anyhow). I haven't had any problems with warping if the boards are cut so the grain runs full-length.