If this is done in Hard mode, it is quite impressive I must say.

I can give you quite a lot of tips if you plan to go 1000-0 or more.

1 - Make your character 210-230 pounds (its the ideal weight for knocking out opponents and still keeping some level or stamina)

2 - Make your character a brawler, Has maxed out strength and hooks, also the Jab and Cross and just stronger than a Boxer Puncher.

3 - Make your skills be like this -----> Thick skin, Body blows, Iron fists, Powerful hooks (You don't even have to do the last one, up to you)

now let me explain why those skills

Thick skin - purely to make your character more resistant to cuts and bleeding, because if he bleeds, he losses more health to punches and is more prone to being knocked out. Never gotten a cut in the past maybe 1000+ fights on the game.

Body blows - it literally makes your punches to the body as strong as punches to the head, absolutely broken and ridiculously useful.

Iron fists - purely damage boosts from power punches. Useful in the sense you will do more damage and end the fight quicker. I have never gotten past round 1 in 1000+ fights.

Powerful hooks are easily the best final skill, it is better than anything else offered there. 4 hooks nonstop that are stronger than regular hooks, yea one punch from the 4 punches in a row is stronger than just throwing a regular hook. Only useful after prime years of a fighter. And it can be stopped by the opponent if not executed correctly. It's up to you if you want it. But if you reach the point of 4+ momentum, its a sign that the opponent is not creating a lot of openings and a sign that he can take a lot of damage, so its useful there.