What length is the blank and what length bow do you want?
is the ipe in the core or the belly? Sounds like it's in the core. I thin in the future you'll find it's wiser to use ipe as a belly wood as it is extremely tough under compression. Nothing wrong with it as a core, it's just a bit heavy and not doing much work there.
How thick are the laminations?
Do you want it to be an ELB style? or are you going to make it more of an american style with a flat belly?
Just off the top of my head I'd say if you want 70#@30", with a hickory belly, you're probably going to need 68-70", with a slightly stiff handle, and nearly (if not all) of the full 1.5" width of the bow (should taper to very narrow nocks ... maybe 3/8"). My guess is and don't quote me on it, is that your bow will probably end up around 3/4" thick with a flat belly ... slightly more with a rounded belly ... which for hickory I would not presonally recommend.