before you start your reno (aircon not installed), please get the aircon man to run the copper pipe (1/4 & 3/8 piping) + 3 core 40 wire to the desired location. You will need a separate isolator at the Aircon ledge for the compressor. The wire is meant for the thermostat which will be located at the tank and that is why you need to run the wire. If you do not want to have the power at the compressor side, you will need to run another 3 core so that you can put the compressor power at your tank side as well.
Having the ID to construct the tank support may not be a good idea as they are not well verse in this setup. A 4ft tank can easily weight 600-800kg and if they just use a plywood support, your tank will collapse in time.
so its good to have someone experience to guide you and to make sure everything runs properly.
1hp compressor + Titanium coil include installation is @ 1.5-1.6k (exclude running the pipings unless the compressor is just beside the tank).
Cheers