Sounds like an interesting feature. I'd definitely love to create an own player. And doing that every 10 seasons sounds reasonable to me. I'm quite attached to my players from my starting-roster. But now after 10 seasons, they're either to old for training or have already reached their cap at Allstar-Potential. So I guess Allstar-Potential would definitely be a good idea. You have a competitive player even in higher leagues (even if it's as a backup in League 1) but he's not going to be the 200k+ Monster that can dominate every other player in BB.
Winner: 1x Consolation Tournament (U21), 2x Goldene Ananas, 1x Goldene Himbeere, 2x Goldener Erdapfel, 3x Bronze Medal (U21)