Regards the Controller we really need more info or a link to the place you bought it from because there are lots of spurious Chinese controllers around.!

Regards the power supply then you'll need a separate PSU for the Drives. Ideally, you'll want one around 44Vdc with those 50Vdc max drives. Don't buy one close to the 50Vdc Max rating because you run the risk of blowing them up, as rule leave a 10% safety margin when sizing the PSU for the drives.

The PSU for the rest of the control box will depend partly on the controller and what Voltage it's Inputs etc will allow and the type of switches your using.
Ideally, you'd want to run your Control system ie: limits,E-stop etc on 24Vdc. This will give you the best protection from electrical noise issues which can plague a machine, esp if using cheap electronics.
However, if your controller will only accept 5V on its inputs then you may be forced to use that. This is why we need to know more about the controller to answer more accurately.

This leads nicely onto the Spindle and Mach3. Same again I Can't really answer without knowing more about the controller board.
Likewise, need to know more about the spindle its self.? Saying 500W doesn't really help because there are loads of 500W spindles which can run on various voltages using various methods to control them. ie: DC with Speed controller or 3 phase spindles with a VFD right down to mains powered spindles like Dremals with no speed controller.

In a nutshell, Often a Control box is made up using several PSU of different voltages. The drives are nearly always run on a high voltage PSU and all the bits n bobs like Limits etc on Lower voltage. It's not uncommon for 5v to be needed for signals and 12 or 24V for things like relays etc.

The Spindle will nearly always be run from Mains voltage, either directly if Dremel type or through some transformer/speed controller/VFD device. Also, some were in the mix often there will a relay used for turning on/off etc hence the other PSU's.

I know it may seem mind-blowing at first but it's actually not that bad when it's explained better, but to do this we first need a little more detailed Info on what exactly you have or are considering buying.