1991 Geo Prizm Oil Filter

You can jack up the car, put on stands, remove the stone/water shield on the passengers side. The filter is under and to the left of the exhaust manifold. The best access is from under the car. It screws into the block horizontally. If you use a Toyota filter, they come with celophane covering the seal, be sure to remove it first before installation.

The smoke on start up is the valve seals, not uncommon in a car this old.
You would have to remove the camshafts (intake and exhaust) to replace, and there is a special tool set you would need, since the valve springs are recessed in the head. You would also need shop air to hold the valve in place while removing the spring/locks.
The spark plug tube seals prevent oil from getting into the spark plug hole, but oil could only get into the engine if the spark plug was loose.

You short Te1 and E1 on the diagnostic link on the drivers side shock tower. This will remove the computer advance, you can then set mechanical advance (10 degrees BTDC).
You will know that you are in diagnostic mode because the check engine light will flash every second while engine is running.
Turning the ign. To the "on" position with terminals shorted will display any error codes.