Trying to maximize ethical behavior under utilitarianism would probably mean getting as much money as you can, and giving almost all (as much as you can, to remain able to do your job) to the most efficient charity. You can spend money on yourself only as much as is necessary to keep the process running; same about free time.

You are correct about the de facto servitude. No excuse for luxuries while someone else is suffering. (Except if you could show that enjoying the luxury increases your productivity enough to balance the spending.)