i can't really help you as i don't know mk3's too well, but on mk2's if the cable has a kink in it, it will be very stiff and this might be part of the problem.
if the heater has been bypassed and is leaking then chances are its a heater matrix and is quite a long job, but not overly hard depending on how clued up you are with tools.
again, not sure on this but if the door handles are anything like corrado's and passats then there is an electric set up that controls the central locking. my passat will unlock the doors from the passenger door, but won't lock them. i'm assuming a new handle should sort this as its specific to that door, a fuse would be fused to the whole assembly.
have a search in the mk3 section for more help.
