For what it's worth: look at the threads by Al Rabe on the stuks forum.
1. he makes sheets by glueing them with thick CA before wetting.
2. he emphazises that you have to compress the balsa all the time! When wrinkles occur , wet again!.
3. My obvious hint: make only one half-buck and use it twice for two shells, arranged mirror wise over the fuselage.
I made a circularly round fuselage whereby the main buckles occurred in the region of the wing cavity, so a lot of excess balsa could be cut away there.
4. Look up the construction story of the YAK by Derge Delabarde. I think it is on a Brazilian Forum.
5. By using Walter Musciano's method of vertical keel building, you make life a lot easier.