Welcome, Prashant. My name is Brandon, and I’m one of the mentors here. Have you read the GSoC Live Blog yet? Many of your beginning questions should be answered there already or will be shortly. Once you do that, check out the Joplin Github issue tracker and get familiar with the code and the build system. Since you are familiar with React and Electron, I can safely assume you know how to use npm and yarn and know how to read the package.json files?
If you have any questions, feel free to reply here. I’m not a programmer, so I probably won’t be able to answer the tech questions you asked above but if you were to check their forum posts, you should be able to find those answers.