is there a way to increase the Visual Description size to something bigger then 400 for custom characters
Maybe? Considering Dev has recently increased description length from 300 to 400 a few updates ago, I'd bet on no. At least not for a while.
Also, if Dev could have done 500 or more, I'd assume it would have been done already. There are likely issues with a larger description.
I'm honestly surprised we even got 400. But it could happen? Dev as been very generous lately with updates.