and am wondering about increasing the water pressure
As far as I'm aware, it's not the pressure in wfp work that does the cleaning, it's the de-ionised water "holding on to" the dirt on the glass and flushing it away. That's why it's important to rinse properly. So long as the water's spraying onto the glass you should be OK.
Look for the blue handle on the side of the pump box and try different positions to see where it works best.
I think that if you fitted jets to the 2 holes where the water leaves the brush, that this will increase the cleaning power
I'm not sure I know what you mean. There should be spray heads fitted in the brush, they're quite flush to the body of the brush so that they don't scratch any glass.
Probably the best place to ask is on Peter's site, or direct with Peter himself. . . . http://www.window-tools.com/cgi-bin/yabb/YaBB.pl The site's more or less 100% again after some recent problems.