Ambitious stuff!
I believe you will do better with 3 steel tubes as your struts, rather than lattices. While the lattice can be much lighter, the drag will be tremendous.
Also the cross-bracing that you draw like this:
|----|
| /|
| / |
| / |
|----|
makes me concerned for the long life of your turbine.
It is definitely NOT the same as this:
|----|
|\ |
| \ |
| \ |
|----|
Although at first glance they may look the same. They are not.
The first design puts the cross-brace into compression. The weight of the blade must be PUSHED up by the diagonal member.
If it is lightly damaged, this cross-brace can collapse. In the resulting imbalance, the turbine will be destroyed.
During normal operation (assuming no damage) the compression load will switch to tension once per revolution, causing an alternating stress that will accelerate the fatigue cycle.
The second design puts the cross-brace into tension. The weight of the blade must be pulled by the diagonal member.
If it is lightly damaged, the cross-brace will continue to bear load, and the damage can be found on later inspection.
During normal operation, the tension load will increase and decrease once per revolution, but the ratio of stresses is much less likely to cause fatigue failure.
You still have to deal with the vulnerability of the lowest brace to compression/tension cycling fatigue, but at least having the cross-brace the right way cuts the difficult problem in half.