You need to do a bit of research before you try growing. First you should read through "the growfaq" theres one here, as well as at many of the other stoner sights, they are as good as free gold.
So to answer your questions:
1. Voltage (vautage) Really isnt what you are looking for as far as lighting goes, the key to lighting is "Watts", and that depends entirely on hjow big you want those 2 plants, and I would reccomend getting a HID (high intensity discharge) lighting system, a 200watt system will do you justice for 2 plants, or you can do 2 big ass plants with a 1000watt, it all depends on what you can spend.
2. I assume your going to use soil for 2 plants, so if you mix the soil right, you should only water them every few days to a week, you gotta get a feel for when they need it.
3. You should only leave the light on for 18/6 hours durring veg, some people say to leave it on 24 durring veg, but 18 is plenty, and theres no need to waste electricity, and 12/12 for flowering.
I hope this helps.