Hi there,
1. That depends, I have a Universal 18ft pole from Chic cleaning ( the orange one) and I have a 30ft Professional pole from Gardiners. They're both great, but your arms ache really bad if you use the 30ft for a long time, but the 18ft is great to use all day. I'd reccomend that you get 2 poles, i use the 30ft only about 3-4 days a month. You can reach anything that you would've done using a double 12ft ladder.
2. Again, that depends. If your tap-water tds ( total disolved solids ) is quite low, ie under 50, you can get away with just using a DI ( De-Ionising ) system, but if the tds is higher it works out more economical to invest in a Ro system.
Then it depends on how much water you need per day, I've never used more than 400 liters in a day, but my brother has used more than 650 in a day. I have a 200 gallon per day Ro from Ro-Man, gives me about 420L in 14-15 hrs. My Brother has a 4040 ro and it can produce loads more.
3. Depends on what you call best value. If you mean the cheapest then just use a by-pass valve on your pump. If you want to maximise the charge/capacity of your battery and have a constant regulated and controlled flow then go for the varistream.
4. Di resin removes the final impurities from your filtered water and removes the ions too, it sorta polishes the water.
How long the resin lasts depends on the output tds of your Ro, the higher the tds the shorter the resin lasts.
5. It depends on how dirty the windows are, whether its the 1st time of wfp-ing, what your flow rate is. See part B to answer to 2 above.
As to your using either a 1000Ibc or a 500L Ibc to transport your pure water, DONT DO IT, they are unbaffled and would be dangerous, get a proper baffled tank and secure it properly to your van/car/trailer.
6. Just read through the archives on this forum, you'll learn a tremendous amount from it, and most of your questions will have been discussed before.
And dont be shy to ask questions.
Hope this helps,
Tim