@CalhauGTi, without tuning you can simply disregard the first point of my original reply. As for the timed races, try to calculate how many laps the race will be based off of lap times. For example,if the race is 30 minutes long and you are running lap and times of 1'35 on average, you can simply divide 30 by 1'25. The easiest way to do this is to convert from minutes to seconds first, this way you aren't messing around with fractions.
For your series tire rules I would use the harder compound at the start of the race if you don't have to use the tires you qualified on. If you do, the I would use the hard tires for the second stint. This way, you are getting that out of the way when the car still has more fuel in it and you can save the softer tires for your final stints when the car is light.
I'm not entirely sure for the engineers in Formula 1 go about that yet, but I guess that's why I'm still an engineering student.
Also, the way you described how you do your fuel calculation can work as well, as long as your L/lap reading is less than 5, in case there is an extra lap at the end which was not anticipated. There are many ways to go about this process and as long as the reasoning is good and the math is correct you should be okay.
I hope this answers your question a little bit better. Have a nice day/night wherever you are.
- Whitetail