Hi Prakhash,
#1. There isn't any specific format or template for proposals. But, do ensure that you put up information regarding detailed project schedule outline, your bio, academic profile, expected deliverable's, project goals and your research/proof of concept on the project idea.
#2. The answer is trivial. KC is scheduled for a release anytime soon. Before you start working on a bug, you must contact community (stianst or anyone on irc) if it makes up sense and needs a workaround. The number of slots are always limited. Bug fixes and good understanding increases one's chances. But, you can focus on academics if there is any stress at the moment. :)
#3. Obviously, you can contribute anytime or any day as per your will and time :)