hot & cold water pipes questions

am putting in a shower cubicle in the corner of the garage and am going to stud up the brick wall so I can run the pipes between the bricks and the villaboard. It will have its own hot water system and water tank as its a long way from the other side of the house where there is water available.

Now the questions :)

1. Do I use poly pipe from the water tank to the cold or convert it to copper somewhere along the line?
2. Can I use poly for hot water?
3. I am guessing I will have to use copper for the hot (and maybe cold) can I use the compression fittings with the olive behind the walls as someone once told me these dont last forever and leak and its best to use the soldered fittings.

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