yes...safe .  no worries  . 

your shower head and cord  should be plastic  /rubber material.    no chrome  finish ! . 

this heater come with  a inbuild elcb ?  test to check if the elcb works. ie trips .
if no elcb ... either you return the heater or install a RCBO  . cos NOT safe  at all.

This picture will tells you why a conductive hose is not recommended. The electrocution comes from the faulty heating element which are in contact with water. A PVC hose is way much safer.

the plastics  pvc piping go up to where ?

i guess to the  water heater  water IN .

yes is OK  as risk is low cos you use a plastic  tube .

No problem for the water inlet, since you just change the L angle valve - assume you will keep the white flexihose.

It is the water outlet (to shower head) part that must use non-metallic (plastic hose).

yes...no worries .