http://forums.d2jsp.org/index.php?showtopic=27247710&f=74That's a good mage welling guide.
If you spend 5k, you can definitely well with 90%+ success rate (probably more like 99%)
When the ladder resets, all your gear stays, but your characters are rerolled. For the most part, your gear will stay the same price--it may change slightly, but it's not like d2 ladder resets.
A muteable is an item which you transmute. People buy muteables and transmute them hoping for something good. Some people sell all the muteables they find and you can make lots of fg from it.