Ok I like your ingenuity and willingness to try new ideas! Carry on
I think the oak could work as a bridge plate. But if it seems like it's prone to splitting, I'd worry. A slab or rift sawn section would be best I think.
Can you make a 3 or more piece laminate neck using some straight grained oak as a center stringer for instance?
The problem with lightening up the upper bout bracing is that this is precisely where guitars absorb a lot of the stress/strain.
With small guitars, I THINK (but do not know experimentally) you could get away with less top braces, such as the finger braces and tone bars. Early Martin's only had one finger brace on each side and there are boutique builders who still follow that on 0 size bodies. The Taylor gs mini does not have tone bars but that can lead to top seam separation (happened on mine).
If you are thinking of making the guitar with a scale length shorter than tradition, then you will have even less tension on the top and thus can get away with less structural components.
That's what I'm thinking anyhoo! Good luck.
Sam