Welcome to FlyerTalk Desperado. A little fine tuning for you here.

I believe Qantas uses the International Terminal for departures and Terminal 4 for arrivals. If that's correct, then from Terminal 3, your departure terminal will be closer by about a minute or two. Please verify your departure terminal in case I'm mistaken. It wouldn't be the first time I've been wrong.

Also, when you exit Terminal 3 (either level) you actually need to turn right and continue on the sidewalk which will curve toward the left and immediately you will see the International Terminal (aka Tom Bradley Terminal) on your right. From Terminal 3, it's about a one or two minute walk. If you do require Terminal 4, continue walking for an additional minute or so and once the sidewalk curves left again, Terminal 4 will be on your right. The LAX terminal map that flyingcat provided a link for is excellent.

And some good news. I've just been advised by Midwest that they will transfer your luggage in Los Angeles to Qantas. You will need to request it in Milwaukee and show your Qantas tickets/itinerary when you check your luggage for your Midwest flight.

Good luck and happy travels!