Decide what type of shower you want, power showers which get their hot water supply from the cylinder are commonly used. But also available are instantaneous showers run from the main service.
You should check with your plumber what shower would be best for you to use. If you have a low water pressure, it would make sense to use a power shower.
Water Tanks
The water tank may be downstairs but it will be fed by a header tank, giving the necessary pressure to push the water upstairs.
Tiles
Tiles can work out expensive, and to tile the entire bathroom is not always necessary. The only parts of a bathroom that need to be tiled are the areas that come into contact with water regularly. The rest of it can be decorated however you want. Fungicide paint is also available to help against mould growth, which could occur from the moist atmosphere in the bathroom especially around window reveals.