1. Most people don't make flash cards, so its hard to say
2. Depends on what you make flash cards for. Are you making them just for the cases? Vocab words? Multifactor tests? Entirely depends on what you are trying to remember
3. I wouldn't spend too much time on making cards if it takes away from doing practice exams or other kinds of productive studying. A good time-saving approach is to not use physical flash cards, but to use computer/phone app flash cards that can be made in a matter of 30 seconds, and then stored on your phone so that you can practice your cards anywhere form the subway to the crapper w/o actually carrying around a big card stack. I used a card app that synched up to a website, so I could make the cards on my comp, and then access them on my phone
I do the online flashcard thing and then use the iphone app to go through them so I'm not confined to the same spot the whole time I'm studying...I have to get up and move.
But I made over 200 for my estates exam. I've made about 100 for my corporations exam. Those are the only two classes I actually made flash cards for. I don't particularly rely on them for studying...I more or less use them when i feel like I'm comfortable and use it to reinforce and make sure I know the stuff. And I do it when I'm tired of reading over my outline for the 400th time, or going over my notes/readings. They serve a purpose but I def. don't really put too much emphasis into them.