You need to know what the rate of infiltration (inches per hour) will be through the turf and the soil above the pipe during your design storm. Keep in mind that ponding will increase the infiltration rate because of the pressure head above it. But hopefully you've designed the turf and soil to have an infiltration rate greater than your design storm. Estimate the contributing area for each junction and solve for your peak flow. You won't need inlets...just set it up as a Known Q inside the junction.