Fan temps to kick on are 215ish for the low speeds, and 225ish for the high speeds. Check the relay if they don't come on. I think the third from the passenger side IIRC(don't bet on me though)
Trans fluid. It takes the amount it takes until full. Since we don't know how much you emptied.. it'* impossible to say. However..I hope you refilled the torque converter before reinstalling it, otherwise, you are probably going to have to remove it and refill. Another indication is that when a pan is dropped and service done, the trans takes close to 2 gallons.
Check Engine light.. need you to get the codes read to further help more.
00 Regal GS: All kinds of cool stuff.