Hi, yes you can put the hot tank/cylinder on the ground floor. They are usually raised just for support,ie across the boards for weight distribution.
Higher the tanks the better the pressure. For every 10 metres you get 1 bar of pressure.
Hi , yes the pressure out of the taps will be the dependent on the distance from the tap/outlet to the tank level. So pressure will be higher on the ground taps than higher floors.
Hi , yes the cold water storage tank. The relative height of that tank to the outlets are what gives the pressure. The hot tank placement isn't important in that regard as the water runs through it with minor pressure loss.