Initially, the flow rate will be at the maximum. As your sections progress, the flow rate will diminish. As you start to return to the last section, your flow rate will start to increase again. If it doesn't, you should check your numbers. You will be asked for this input at each section - since it is not uncommon to transition from steel to copper when you are using the smaller pipe sizes.
Copper tubing is much easier to work with also.
Please note that you can only use one pipe size per section - so if you transition to a different size you must make a new section. The pipe sizes and recommended flow ranges will produce friction losses in the range of approximately 1-4 feet per 100 feet of length. In the larger pipe sizes, this velocity restriction is relaxed - so you will find the allowable velocities are much greater. Despite this, you could produce Reynolds numbers greater than 3000 but still have ridiculous combinations of flow rate and pipe size. But only a fool would design such a system - because it would be so oversized and expensive.