1, yes,
2 I would go for a 27' Clx
3, one brush can do all
4, you dont need chemical to clean a con roof, although it can make life a whole lot easier on some job, you can use the same brush for everything, to get chemicals if you choose to use them, I would recommend you get a hand pump sprayer a harris pole and some tubing (no need for ladders then.
5, I would have a small ladder for gates, should you need it, small enough to fit inside van.