Hi Ujjwal,
Happy Holi. Great to hear of your interest, it seems that your experience will help with this project.
We want to only use existing devices -- your work should be in determining device bluetooth API, and connecting these devices to your phone and OpenMRS. You shouldn't have to do any actual hardware/soldering work, as the deliverable is the app itself.
Yes, do start with the proposal. The earlier it is on GSoC, the earlier we can give feedback.
We intend to work with devices the patient already has.
As a start, I might visit your local clinic to see what devices their patients are using here in Delhi.