Calibrating tips is nice but not necessary. Just make sure the tips all have a good pattern. Remember that your rate controller in auto mode is going to put out X GPA no matter what and it will try to maintain that. Sometimes if your filtering becomes plugged, you will see this as an increased pressure on your gauge but the system will still try and maintain the correct GPA that you have it set for. If you tried to adjust your pressure down manually in this case, you will not be applying enough product at the nozzle tip and you may even lose your pattern!
That is the beauty of the auto rate controller! Let it work for you. Generally I only go into manual mode when I want to spray a heavier rate. Example a patch of weeds or a corner of the field. You can increase the amount of product going out, simply by switching to manual mode and driving slower. There are other methods as well by changing the actual rate but I find that it is very beneficial when cornering your first round on a field to slow down so that you get more chemical at the outside end of your boom tip since it is traveling way faster than the opposite end. You also have more control so you don't run your boom into a fence!
About the accuracy - it isn't great with a paddle and ceramic shaft but it should give you 5% or less application error. I was never impressed. I always monitor every tank I fill that goes out to see if I get the right amount of gallons out of it. It varies greatly. I used to have a Teejet 844 rate controller which had an Italian turbine type flowmeter mounted on stainless steel bearings. On a 1600 gallon tank, it was generally within 4 or 5 gallons of the load! Flexicoil on the other hand is generally within 50 gallons or less on a 1600 gallon tank. (To me monitoring the total tank is critical because the flowmeter should be able to count your total gallons very accurately if it is calibrated correctly. If you have to be mindful of how much is left in the tank which sometimes when you check, you need to turn off agitation etc. in order to prevent frothy glyphos mixes etc. I always evaluate what I think I have left in the tank!)