if you want pretty coins, maybe you can live without 5000 in each level? in mario, it took forever to find 100 coins in each level, and you want 5000 coins in a single level?
if you really need that many coins, i would forget about reflections and proper shadows, turn off reflections and shadows, add a blob shadow decal and fresnel rim lighting shader, or just make it glow and call it good enough. if your game involves collecting 5000 coins in a level, i doub’t the player is going to pay too much attention to each coins reflection and shadow quality.
if all else fails, add a sparkle particle effect and a nice sound effect, and it should feel great.