My first advice is always to call a qualified electrician. If you insist on DIY then here is the best I can tell you with the info provided. I cannot insure that I'm providing the knowledge that is gained from a 4 year apprenticeship progam. I don't mean to sound
antagonistic, but only try to convey the gravity of your safety and the importance of proper electrical installation. Although a small project I can no way cover here all the required elements.
Question 1 answer is maybe.
The ampacity rating of the existing
circuit, the existing load on the circuit,
the wattage of the new fixtures,
and the number of wires in the existing box.
Question 2 answer is yes with the same concerns given for question 1
Question 3 Clarify
You run the wire from each fixture to the switch "BOX" in the the box they are connected via wirenut to a pigtail and the pigtail is connected to the lower terminal
of the switch. The hot is connected to the upper terminal. Again provided you don't exceed conductor fill in the box. You can also daisy chain from fixture to fixture
either using a J-box @ the fixtures or fixtures approved for such.
This is all taking into account you understand all the other requirements of doing the installation. IE
Size of boxes, size of wire, type of wire,type of fittings,
strapping requirements, box sizing requirements, length of wire in boxes, amount of insulation to strip, correct wire nuts to use and how to properly put them on, routing requirements for cable under floor joist, grounding requirements, wire color for switch leg, etc etc etc etc
If you do know all then proceed, if not keep reading your wiring book. It's always a good idea to get a permit and inspection. If you are a novice in wiring but want to DIY it's a good idea to have someone qualified take a look at your work before you enegize. And remember to turn off the breaker and check with a tester before making your final terminations.
[This message has been edited by TE (edited September 13, 2002).]