Hire a concrete pump and have it delivered, pre-mixed, by lorry.

Would that work over a 45m stretch? Which is the distance between
front and back garden where the wall is.

How much concrete would I need for a 27' wall high of 4'1/2" for 18'
then sloping down from 4'1/2"to 1' high for 9' ?

Would I need a different concrete mix to get a smooth finish once the
the ply was removed so no rendering was needed?