A beauty! I know some bowyer wanting to do a similar thing with detachable limbs, if you do not mind me asking, in what manner did you attach the limbs? Any tips to prevent cracks ? Sorry if this is out of the blue, but your post made me think of them so I immediately remembered your thread. Anyhow, much good shooting to you, those specs are very decent for a first bow! 
I attached the limbs with the kit from Bingham Projects. I felt the pins were a bit short, but they did work on another riser. For this riser I used some spare bolts and washers I had laying around for the attachment closer to the limbs tips.
As far as cracks in the riser, the bending moment is pretty severe on a riser. Reinforcement should be continuous on the back of the riser. That is to say continuous wood grain as opposed to exposed end grain (even if the contour cut into the riser is mild). And it goes without saying the material should be thick enough that the riser itself is not flexing. All that being said, please keep it in the context that I have only built two risers
This riser (fingers crossed) has shown no issues.
The other riser I mentioned above did start to crack when it was as shown in the first picture below. Note that back laminated veneers barely extended beyond the lower laminations and exposed end grain. It cracked at the leading edge as indicated. The limbs on that bow were heavier and recurve, so the demand on the riser was greater. And yeah they were fi***gla** but we'll ignore that...
I repaired that riser as shown in the second picture, and it has been holding up without sign of issue for several hundred shots thus far.
As far as the belly side, I made no particular efforts to reinforce it as seen from the final pic.
Hope that helps, but if I misunderstood your question, feel free to let me know.
