The past two seasons we have used 1/2" Baltic birch for our bellypan/electronics board. We haven't relied on the wood for holding the frame together, but more to help add rigidity. We even used it 2012 to made custom 10" wheels for the drive train.
We typically only put holes in the wood if we are using them. From the photos, you may want to eliminate some of the unused holes near the high stress area. You may also want to look at distributing the load on your hard stop mount. Are you using a large fender washer? Could you make a quick 'glorified' washer that has an additional mounting hole about an 1" or so on either side of the main hole?
Another nice thing about wood is that it is very easy to use a
router to recess things or "pocket" the wood.