Hi,
I do not know if this will help much, but, I live in the UK and have a lot of experience making flatbows successfully with Ash. Living in England I am assuming it will be near enough to the Ash we have here? You say its called european Ash??
I do not get anything as near as wide as those logs you have, but, I generally split my logs as soon as I cut them and take the bark off and seal the ends with PVA glue and leave it a month and then work the Ash down slowly to near finished bow by floor tillering slowly and let it dry as I go. Just have to be careful with the floor tiller and not bend it too far while its still too wet. You could damage the wood on the belly if you push it too far, too early. This staggered approached has worked for me with the Ash I work, when it is drying.
My ash bows are normally between 2" - 1 3/4" wide for the limbs from the fade to mid limb and then taper to 1/2" nocks in width , 4" handle with 2" fades wither side, so you have 8" non- working limb area and about 32" for each limb. That gives a nice over length of about 72". By keeping Ash long and wide like this, you are increasing your chances of success to make a bow that won't break on your first attempt. Taper the thickness of the limbs from where the limb begins at the fade to the nock. It is really important that you get the thickness taper correct, spend a lot of time checking the thickness taper over and over. IF you do, the tiller will be correct, as Paul Comstock said 'good taper is good tiller' and he was right.
Make your handle about 1" thick or a bit more if you want. I normally make my handles about 3/4" wide, you can get away with 11/16" handle width if the handle is deep enough.
This is the style of bow Paul Comstock teaches people to make in the book 'bent stick' using white woods. I have a library of bowyer books and I have to say if you are working with Ash or any white wood, this book really is the easiest to follow and best bang for your buck as a beginner, I strongly recommend it.
If white wood will be your future go to wood, long and wide flatbows provide fun free shooting with low set. If you have a real fetish for longbows with stacked/deep bellies, I would not suggest you try it with your Ash as a first attempt, in my humble opinion. It can be done with Ash, you just need the correct wood and a lot of heat treating.
Good luck with the Ash,
Dean.