The first thing I would do is see if the tach is bouncing while you crank the engine. This will tell you where to look next.
If the tach doesn’t bounce while cranking, then you’ll need to check the timing belt and the electrical plugs going to the distributor (verify you have +12v on the black/white wire with the key is in the run position). If these check out, then the issue will be the ignition module inside the distributor.
If the tach does bounce while cranking, then you will need to check the electrical plugs going to the distributor, the distributor cap/rotor, the coil, and the wire going from the coil to the distributor cap.
As for the oil gauge, I would check the electrical connector coming off the sending unit on the back side of the engine. The electrical connector is notorious for corroding and causing intermediate oil gauge readings.