1. Get H4, if ur sister apply F2, soon or later she will transfer to H4 anyway. As long as marri
ed, not difficult to get either one.
2. Usually >= 3 yrs, you can still visit china cuz u have GC already.
3. Need financial statement (at least 1yr tuition+living), not difficult to get visa, if failed,
 just schedule interview again and again..