Kinematic Hardening is better for stent simulation than Isotropic Hardening because the operation of a stent is generally that a balloon expands it against the artery wall, and the the stent experiences a reversal of strain when the balloon deflates and the stretched artery pushes back against the stent.

The Yield Strength for Steel can vary over a wide range. You said the Yield Strength for your stent material was 470 MPa. You should use that.  Even better if you have the Stress-Strain curve for your material.