Ya 2 1000watts with a 100 gallon rez will be fine with out a chiller. What you could also do to save lots of money. Is buy a radiator from a car make sure its clean. Put 1 or 2 fans blowing on it and make the water run through it before it goes back into the rez. Works wonders and you could pick up a radiator from say a ford truck or something for much cheaper then a water chiller.
And no i wouldent suggest running the same rez your nuts are in it the glass on the lamps still heats up and you would get nasty build up on the glass it self. Also i put pool chlorine as suggested in the rez with the water used for the liquid lumens. To avoid ANY kind of parasite or what not growing in that. I actually stoped using chlorine cuz it started to eat away at the water fittings attached to the relfector it self. Bought Pythoff ( http://www.flairform.com/Products/pythoff.htm ) works just as well and dont have any problems with the fittinfs at all now. Hope all this helps. Happy Growing .