I also agree that these changes should be kept for next season. Also, why not have both a reserve character and a coach?
Eh, well good question...
I think, as I'm really bored, I'll elaborate a bit on the custom characters:
New Character:
Name
Right-Handed/Left-Handed
School
Starting Points -> As I said earlier, we could use this to balance things out. E.g. when we agreed on all new rules and maybe teams, we make a list, where each team is ranked. Afterwards whoever is first on that list gets a charcter with 6 points, the one who is ninth gets one with 15 points or something. Then, whenever that character is used in a match and wins he gets a boost of 3 points.
Feats, Effects etc. -> I'd propose you are gonna receive these when your character reaches a certain level. Also, everyone could get a Feat of either Singles Expert or Doubles Expert in the beginning.
Playstyle? -> If we were to give every custom character a playstyle (offensive basliner, defensive baseliner, serve & volley or all-rounder), we could adjust the effects and feats you can receive based on this.
I think that's all I can think of for now.
A coach wouldn't actually too bad, but it's quite limited. You have
Banda, Ryuzaki, Sakaki, Sanada, Yukimura, Echizen, Tachibana, Mizuki (omf XD), Jyousei Shonan one? Midoriyama one? Oji, the fat bald one from Higu, Watanabe (Shitenhouji one). MOre then enough for one each, guess we cant pick the player-coaches that we have on our team obviously.
I don't think player coaches would be a wise choice. Imagine Sanada would play a team with Sanada as coach. Definite no from my side.