Hi.
I think the most important wrapping is the one that just goes around the aluminium part in wing. Gluing aluminium directly to wood spar is a little unsafe, and the wrapping (Kevlar) between these 2 materials strenghten the glue joint a lot. After that you can add some Kevlar and wrap the Al part and spars together but it is not absolutely necessary. Actually, if there is no gaps in the assembly, cyano glue is strong enough.
For gluing aluminium, I know there are products and methods for etching the metal or anodizing it to improve glue adhesion but I have never really bothered with those. What I have found sufficient is:
-Good de-greasing with acetone.
-Surfaces must be roughened with sandpaper. The problem is, that when done dry, aluminium surface very quickly oxydises, which weakens the glue joint. To prevent this, I first apply glue (slow curing epoxy) and then sand with #80 paper. The epoxy acts like cutting fluid and it prevents the contact between oxygen and aluminium. It can get messy but so what.
-Whenever possible, the epoxy should be cured in raised temperature. That would be about 50-70 degrees C. When the other part in the joint is wood, the ultimate strenght of epoxy is not the most important thing. The important thing is, that in raised temperature, epoxy's viscosity goes down and it penetrates deeper into wood.
When gluing two differend materials together, it is better to turn heating off before the glue hardens completely. Especially with long and narrow parts (I'd say over 50mm long). There, the problem comes from differend thermal expansion of differend materials. If the joint is let to harden completely in raised temperature, there is a risk of warping or at least a shear tension inside the joint. L