Sam what generator is involved, what type, size and rest infos ?
For voltage you can go with voltage divider or small transformer.
Current measuring hall sensor like A1302.
For fuel level, you must describe generator and fuel tank, all from shape, volumen,...
Its possible to count and log produced KW/h, measure temp, log data to eeprom chip,.....
Also current consuption of fuel can be measured by specialized sensors which measure fluid flow.
Check manufacturer recommended way to stop generator or see how they do this. This can be different if generator have electro starter with battery and its on gasoline or diesel. Maybe generator is small sized and dont have battery and electro starter then situation is simple.
Just one remark, be careful and dont play with powered wired near fuel tank, even on low voltage as 3V or 1,5V. In these situations voltage is not counted, only thing what is counted is spark.