5 mm thickness is scarily thin for a belly. It leaves you very little room for tillering. If you remove too much ipé on the belly during tillering, you'll make it too thin, causing the belly to collapse. It would be good to use a thicker belly lam of ipé. However, if that lam is the only one you have available, you can design the bow accordingly. You should focus on as little tillering as possible. That means the backing and core should be pre-tillered before they are glued up. I would highly recommend a tapered core. A bamboo backing of 4 mm thickness of also a little too thick, I think. 2 mm is very well possible, but 3 mm is about the maximum I personally accept. I'm a firm believer of 'the thinnest bamboo is the best bamboo', but others may disagree. I think you should taper your core, and aim for a total thickness, of all laminations combined, of about 15 mm. near the handle and 12 mm near the tips.
I'm actually currently working on a BBI R/D pretty similar to yours. It'll be around 70" in length though, and about 40-45 pounds. It seems my total limb thickness will be around 11 or 12 mm in most places. A powerlam stiffens up my handle, though. Except for this powerlam, I don't use a core. My ipé is only one lam of 11 mm. and the boo is about 2 mm.
Hope this helps.
Jorik