Ideal settings for regulated power using Arduino Uno VIN?
Honestly, it doesn't matter how much power (amps) you make available, it will only draw what it needs.

However, there is definitely something to be said for limiting how much power you provide.  If something in your circuit is miswired or otherwise shorts out, limiting the circuit to something reasonable (wisely including a fuse in your design as well) means that you won't have some enormous current suddenly passing through burning stuff out and possibly injuring someone. :)

As far as what to provide in terms of volts and amps, the data sheet for your particular arduino is the place to go.  As long as you are providing that you are in good shape.