As early Down Throw conversion, D.throw > Full Jump D.air > Air Jump N.air, is true from 0 to 40%.
It's one of the most reliable and easy combo to practice and add +23% to your down throw (30% without pummeling).
Pit's true combos are listed in this guide
https://smashboards.com/threads/an-in-depth-guide-to-pit.473370/
Pit N.air hardly combo in itself. It will often be the last piece of a string to catch an option in which case an Auto cancel N.air can reset a string.
About strings mix up, none of the following are true combos.
D.tilt > F.air can be repeated few times. Characters with high falling speed or big characters can be stuck in.
D.air can sometimes position for another D.air, F.air or Up.air.
F.air to F.air out of stage can steal some jumps and the stock.
Above 50% most of your conversions will become 2 move true combos and tech chases.
The D.Throw > FJ D.air > AJ N.air will get you to these percentages in a blink of an eye and then all left is spacing, read and punish.
But remember one thing : Pit is not a character who likes mashing buttons.
Although he got decent disjoints F.air, N.air and Up.air are all low damage multi hits, any aerial trade with these will greatly reward whoever character plays your opponent.