the ease of door replacement depends a lot on the hinge type.
if the hinges are on the door itself, etch around them on the car before you remove them, especially if the fitting screws sit in slots rather than definite holes (if that makes sense) it will give you a near perfect fit first time.
wiring is easy enough as there should be the same coloured wires on each door. if they are from different years, there could be differences in wire colour but on a ka there is probably only speaker cable & potentially central locking or electric windows depending on model.
as others have said, trolley jacks (or even a couple of decent chunks of timber) for taking the weight of the door & an extra pair of hands to hold it will come in really handy & knock hours off the job compared to balancing it yourself.
make sure you leave the passenger door open / unlocked too. a mate of mine managed to lock his keys in an old mk2 golf when we did a door transplant as he didn't realise the door pin was down when he closed the passenger door to check the alignment!