Solved

League change penalty

It sounds like he did choose the right time to leave the old league, between the last race of the old season and the first of the new. In terms of money penalty that shouldn't have happened for two reasons. In the space between seasons there shouldn't be any money penalty in the first place and as far as I know it should be still disabled in any case. So I'm pretty sure once Yunus reads this he will fix it by paying the money, or token equivalent, back.
The car design resets every time you change leagues, or quit and rejoin. There's no way to avoid that one. Because of this the best time to join a league is at the very beginning because that's the point with the least handicap towards the competition and leaves enough races to catch up and still have some left to compete on equal terms, as much as the team level allows at least, towards the end of the season.