There is some question over whether heat treating is actually anything more than a method to remove excess moisture. Invariably the material will return to the ambient level, but heat treating either removes excess moisture above ambient, from growth or storage, or it lowers the moisture below ambient to a more favourable range, depending on the ambient range. Flaming by itself is just rough and ready heating. People like it the look also.

I make bamboo rods but haven't made a bike. If it was me, I would get an aluminum BB and use carbon fiber to make the connections, or glass. Not sure this is an app where the benefits of carbon are required, at least for initial experiments. Carbon is always lighter, but since it isn't the stuff the bike is to be built of, it may not be necesarry. Some of that Rutan tow that Aircraft spruce sells might come in handy.