Carrying water:
You could carry 4 25litre containers in your van/boot, and they only cost about £10 each. Hurts your back lifting them in and out a bit.
A 1000 litre static water tank to put in the garage costs around £150+vat
Poles vary according to what you get. An average 18ft Fibre glass pole (which will reach almost all 2nd floors) costs around £120. A 30 ft (which will reach almost all 3rd floors) costs around £150
RO units: Vary greatly according to output. A good pump assisted 300gpd system which will be more than adequate for what you're talking about costs about £580.
The amount of water used varies a bit too. I average about 10-15 litres per house, and dont use more than 200-250 litres per day. Its a little bit personal preference though, some people like to use a lot, some less. On first cleans, like Dennis says, you use more. It is important to be able to vary the flow, whatever system you get.
-Philip
PS Check your PM's, I've given you some more info too