I would fill it to 1cm or 2 below the top of the base
Depends what substrate you use as to whether much falls out. I think with any cage you always get a bit kicked out but I wouldn't worry about it. Savic cages tend to be good quality manufacture so I don't think there'd be any issues with paint rubbing off - no more than any other cage over time or any sharpness if it did. And as Alpa says, they are unlikely to bar chew in a 100cm cage. Our Syrian did a teeny bit, for a day or two when he didn't have a wheel - once he had his wheel in he didn't.
I posted on your other thread about the cage too