Is there a downside to providing a lot of amps to Arduino UNO's VIN? Is there any advantage to only supplying a limited amount of amps? I have a regulated power supply and I'm curious what I should set it to when going through the 5v port?
Also, should I stick with 5 volts? I've seen some tutorials say if powering the board through VIN it should ideally be much more than that?
Is there a spec sheet of sort that tells you this?
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.
From https://www.arduino.cc/en/Reference/Board :
The input voltage to the Arduino board when it's using an external power source (as opposed to 5 volts from the USB connection or other regulated power source). You can supply voltage through this pin, or, if supplying voltage via the power jack, access it through this pin. Note that different boards accept different input voltages ranges, please see the documentation for your board.
For specific values, visit https://www.arduino.cc/en/Main/Products?from=Main.Hardware and select your board, and look down to where it says "Input voltage" - there's a "recommended" and "limit", each being a range. Note that some power sources will fluctuate (e.g. 4 AA batteries are 6 volts, possible slightly higher when brand new, but will drop down if there is a high drain, or as they get used up. 4 AA batteries will not provide 6v for long).
As for current (measured in amps or milliamps), if the power supply cannot supply what is used by the board, it will overheat; if it provides more than is required, then it will work 100% perfectly well (so long as you don't have a short circuit). The current an Arduino on it's own will draw will vary depending on the board, Nick Gammon measured an Arduino Uno Rev 3 board at 50 milliamps, but LEDs will typically draw around 20mA each; motors will draw a lot more. 1000mA = 1 amp, so Nick's Uno would draw 0.050 amps. Power supplies typically say on them how many amps (or in some cases, milliamps) they can (safely) provide.
Input Voltage (recommended) 7-12V