hi! - so much i can say: i have made bows using the same sort of limb cross-section; back and belly layer of bamboo, core from vertical bamboo sandwiched between two hardwood stripes. i have learned that from jaap in a clinic he led in germany last summer.
also i learned from him how to use rope and wedges for both gluing the bow up and reflexing it at the same time. yumis are neither made on bowforms nor are they tillered after the gluing process; jaap's video 'all tied up in bowmaking' will show you the rope and wedges method quite well.
the form of the yumi is something quite tricky: not only is the bow heavily asymmetrical and needs to bend in certain ways at certain segments of the limbs, but also is the string supposed to be off center - off the bow to be precise - to the right (seen from belly side) as shown in the picture you posted. the bow can therefore only be shot using a special glove or at least a thumbring.
i would recommend to try a normal longbow
(maybe check:
http://www.primitivearcher.com/smf/index.php/topic,1824.msg22429.html#msg22429 )
or double-curve with this sort of limb cross section before trying a yumi to get familiar with the technique.
frank
