Based on other models, I don't know about yours -
#1 lamp: Temp, (boilover warning). It only lights if overheating. (on some Yanmars it lights when cranking the starter, to verify that it works). You can test the bulb. Go to the temp sensor near the top radiator hose and slide the connector up slightly, then slip a grounded wire in there. Grounding this circuit should light the dash lamp.
#2 No Oil Pressure warning. Cranking while using the compression release (pull the dash lever in front of your left knee), the lamp should go out after about 10 seconds.
#3 Alternator. Lamp should light when key is on before starting engine. May flicker faintly at very low rpm, otherwise off while engine is running.
#4 an empty hole on mine. Yours???
Lamp in face of dashboard, and potted relay on firewall: likely related to Thermostart. (manifold pre-heater). The older Yanmars didn't have an indicator lamp or that relay (timer?), just a manual button to press to run the Thermostart (7~10 seconds), or a Twist-Key-Left position on the ignition switch for the same thing. If you are concerned that those components are unrepairable you could wire yours using a prior method.