Yes i would also go with a MH VHO/T5 combo, like two 250W MH's with 2 VHO super actinic supliments giving you some where around 700 Watts of lighting...That would give you around 6.5/watt gallon, or you could go with the 175watt MH's if your tank is long. I"m assuming your tank is 48"x 24"x 22" since you have at 48 Inch long light right now.
You could possibly find a good deal on one in the for sale forum. To me, I have always purchased the best light and skimmer that I can and then let everything grow into them. If you buy a light for your immediate needs, you will wish you had gotten the bigger one later on, when you see some coral you want....and the person ask you..."what kind of lights do you have".
As far as the Quarantine tank goes, I wouldn't waste my money on one at this point in time. I have never used one, and try to concentrate on only buying healthy specimens and ultimately keeping a very healthy reef. Since there is no way to always buy healthy corals and fish, you can contrate on keeping a very stable envirnment where your specimans can flourish.
Good Luck.