Daniel
I usually have it at neutral at the start. Is that
Pl is track and weather dependent. There are tracks where you can race at pl4/5 regardless of weather and not overheat and others where pl1 is needed most of the time.
You gain knowledge for each track over time through race experience and taking notes. Generally, in live races you need to be managing your pl dynamically throughout the race (high push into fast corners and low push on straights and trying to keep temperature within sweet spot etc). Personally I used to go high push for first half of lap 1 and then reduce, but as I said it is track dependent