Hi mate, Congrats on getting your first bow underway. Good choice to make it a straight longbow too - it will go well.
I build my longbows to 68" for a 28" draw and using an 18" riser, so any stack thickness I could tell you may be more misleading than anything....there are others here who will be better guides for that.
There are two things I would mention though - for 40lb draw weight, you will probably find that .040 glass suffices - plenty strong enough and providing a lighter limb than one with the thicker glass.
The other point is regarding your proposed thickness and width taper rates: The thickness taper is appropriate (although probs at the 'most tapered' end of the thickness taper scale), but I would make the widest part of the limb 1 1/8", tapering down to 1/2"at the tips. If you tapered your width from 1.5" wide, my concern would be that the limb would be overly 'whippy', and that the inner limbs would not be working or flexing enough.
All the best - remember to post photos!
Darren