New amp won't fit into the boot space where the OEM is, because the OEM amp is rather small.
The time consuming part is routing wires, because most of the plastics will have to come out.
When Madmarky and I helped install AmyZeds audio gear it took two of us two days to complete the job which consisted of
Double din HU
second screen
Reversing cam
New speakers in doors
New speakers in rear
New sub
Custom building a box for sub
Two amps
All the wiring
Most audio installs are the same in terms of wiring, the only difference is where the wires go.
For the zed there is actually an unused pre-existing tunnel on the passenger side, which is perfect for power cables.
Central tunnel is perfect of HU to amp speaker connections, once you get the rear plastics out, there is plenty of room for plenty of wiring.
Like many, you could reuse the OEM sub location for mounting you amps and then run an under strut box or something boot based.