Couple suggestions for the problems.
Door latches on older cars often went without lubrication, try some penetrating spray lubricant first - followed by the regular maintenance of penetrating spray grease later. Cold weather & dry, sticky lock mechanism doubles up on this "simple" problem.
Driver side speaker could be a wiring fault where the wire flex leading to the door. Before digging into wiring, look for a plug-in joint where the cables lead to the body (inside the opening between door & body). Just unplugging there, checking for corrosion & plugging back in securely may solve the problem (did on mine).
We don't have the electric front defrost, like the rear checking fuse & looking at wire connector the the windshield would be first checks. Careful with the connection to the Windshield - hold window side when touching the connector so it doesn't pull off the window!!
"Rubber Side Down"
S.R. #275 Focus Takeover #003