My answer will be different from your answer, $300k.
The PDT rule affects US accounts < $25k, so if you start with $25k and lose $1, then you are below that rule, so I don’t know why people start with just $25k USD.
After the years of trading, I would say the key is to get the right mix of equity and skill. You don’t want to be a newbie managing a big $$$ account, you will lose your shirt. You don’t want to be an experienced trader trading $25k either, you will get incredibly frustrated with the position size limited by a small account.