I always wind 10 bobbins when starting a new project. When I use all the bobbins, it's time to clean the machine and get a new needle put in it. Keeps me from having to remember the last time I did it! When paper piecing, I wind 5 bobbins instead as my needles dull a bit faster.
I have 3 machines and keep bobbins wound for each machine seperate so I don't get confused.
Also, I use empty TicTac cases for the used needles, when full just toss in trash can. No pokes or holes in trash bags.