1. Yes
2. Not necessarily. Where the idle timing ends up will depend on where you have the advance timing. Make sure the advance timing does not go past it's slash mark (to the left of it). If that means placing the idle timing more towards the right side (retarded) of it's range, then so be it.
3. See above
You have to understand a little about what your advance unit does and how it operates. It is built to advance the timing a set number of degrees (when new), something like 25. That means that where ever you have the idle timing set, full advance will be 25° from there. Like I said, this is when the unit is new. As it gets old and wear sets in, the amount it turns and advances grows. Instead of changing your timing by 25°, it will move it like 26°, 27°, eventually maybe even more. That 3° or 4° range for the idle timing allows you to compensate for this wear for a while. Eventually, the wear will become too great and you won't be able to get both advanced and idle timing at their specs anymore. Then you need a new advance unit.