The bolts that you have is tronger than needed, but certainly fine. A decent quality stainless steel bolt will easily handle far more torque than ever recommended for a bike application and won't rust. I'm a fan of stainless steel bolts for those reasons.

I've bought boxes of 50 M5 bolts for for $5-7 from McMaster-Carr, so I have bolts to replace anything I might need.