For ipe you want narrow, 1" to 1 1/4" max. As far as thickness reduce the ipe until both limbs are bending evenly and together at the draw weight you are aiming for. Leave the handle area the full thickness(assuming it is 3/4")and taper to 1/2" at the tips to start. Leave the handle full width and begin tapering from the handle to 1/2" tips for now. The tips can be reduced to 3/8" or less later.
When I tiller a bendy handle bow I tiller the limbs first then bring the bend back into the handle during the last few inches of draw. I like to feel the handle give as I hit full draw.