Yes you got both parts correct, though you should brush up on your units.

You did better than the OP here.

Finding temperature before combustion
It would help you if you are able to reason out the method without needing formulae

I worked this way

Work out 500 kJ/s

Heat loss 120 kJ/s

total 620 kJ/s

This was provided by a change in internal energy soley due to a drop in specific enthalpy.

H1 - H2 = 3095 - 2660 = 435 kJ/kg

So to provide 620 kJ/sc there must be 620/435 = 1.425 kg/s flowing.

If 1.425 kg provides 500 kJ of work

So 1.0 kg provides 500/1.425 = 350.8 J of work

Does it matter how long this takes will you get more work (not power) if it takes longer?