Any advice? Does he need silence? Or ability level? I m really confused...

I wonder how Silence affects Physical hero

He needs silence resistance more than the other one (I think it was killing bonus resistance). His ultimate is magical, so even that small percentage is better than the other.
And I would choose ability level rather than the other 2, better for him to dodge more and deal a little more damage than a micro percentage of not be semi stunned or to be less sleepy.

It really depends on the arena teams in your server on how you should build the academy. Study the teams you fight in arena and build his stats to counter them.