I'm not certain of the exact numbers, especially seeing as they changed the formula recently I believe. However, at least to #4 that's not possible. You will never have a 0% likelihood of breakage. Additionally the longer a round lasts, the higher the chance on each tick of something breaking.
As long as you have 100+ wpf and your gear is around 35k you should be making money on average (assuming you aren't an archer that is, as arrows have a vastly higher break chance than other equipment). You will, however, occasionally have bad streaks and lose money with this much gear. If you want to constantly make money, then 20-25k is a good place to be at. As a general rule of thumb try and keep ~20k saved up at all times for when you hit a bad streak.
A lot of this also depends on your multi of course. If you're rolling x5 all day you can afford far more gear than if you're sitting on x1.
