John I wouldn't take the hose to any part of the car with bare metal. If your refering to the phospheric acid cleaner stuff, I'd just wipe it down w/o water.
Thanks. As most people do it here, I would do one side at a time. Only cut out where your going to be working. If you do it like that you wont have to worry about the front end flexing .
Before you start cutting, make plenty of measurments of crossmember location, t/c bracket, swaybar, etc.
Another thing is, If I were to do it again, I would have taken all of the paint, undercoating seam sealers, etc. all at once ( on both sides of the metal). Its such a PITA to go back and remove the crap before you work each time.
Lastly, where a respirator when welding. I can't stress enough how bad all the crap on the old metal is for you!