1) Easiest way to check is to count the number of expansion slots the case allows for. If the case only allows for four expansion slots, it will only accept a MicroATX motherboard. A full ATX motherboard will not physically fit within the case.
2) Not entirely fool-proof, but if you look at the rear of the case, the power supply should be held in place by four screws. Three screws in a corner of the power supply. The fourth will be off-set from the corner.
3) Good to go.
4) Chances are they will not match up with your new motherboard and each wire will need to be connected to the new board, individually.