Can I power multiple devices from a single power supply?
4x devices that are rated as 5v (1.5 amps normal load, however during high loads can require up to 2 amps)
1x raspberry pi
I've sourced a power supply that takes 240 AC mains supply and provides 5v @ 8 Amps.

The RPI can see up to 1 Amp draw, or higher. Some take 0.5A by themselves with nothing plugged in.
So you have a system that takes 6.5 Amps normally, but can jump to 9 Amps during high load.
8 Amps is less than 9 Amps.
So No, that supply isn't a good choice for this.