The label should give you ratios for target weeds. I’d select the rate appropriate for the most difficult target present and am start there. Gallons per acre will vary wildly from individual to individual based on equipment used and the speed and efficiency of application.
My best suggestion is to give it a water only test run. See how many gallons you use at a given speed to cover x-area. Apply that to your equation with regards to how much product you need in your mix.