Whatever you have at hand which will supply the the voltage and current requirements of your circuit. There are no hard and fast rules. You want it to be clean and stable; that's about it.
I picked up another 741 today and plugged it in. Looks like the circuit is actually working but I'm getting too much current for my guage. It's idling at about 85% at idle and the network activity isn't really moving the needle. Maybe I need to look at trying a different router.
Try adjusting the feedback trimpot. This will control the gain of the op amp. If turning it down doesn't give satisfactory results, you might need a higher-value pot.