Adding a new switch and light to an existing circuit.?

That is exactly how you should take the power to your new switch. The only trouble you may run into is if your circuit has a large load on it already. The only real way to know how many amps that circuit has is with an amp meter. Most of the time adding only a couple of lights doesn't increase a circuit load all that much.

When I add lighting for people, I normally try to stay within the same stud cavity. Cut in a box made for installation into existing drywall, bring power over from the existing swith box, and use it for the new switch. In your existing switch box just wirenut your new power feed together with the power to your old switching. I doubt that you will have any problems with overloading that circuit. If overloading occurs, you may need a new circuit from the panel, but chances are you'll be fine using the same circuit as the existing lights.

Adding A Light Switch

You need to get the new wire from the new fixture to the switch box. Once you do this by cutting a hole in the drywall and fishing the wire you should be able to do what you want. The hardest part is putting the wire in to the wall and running it to the new location. Then it is a matter of connecting the conductors. I suspect that you will need a larger connection box since you will over fill the current one when you add 3 more wires. Your box fill needs to computed before you make the decisions. Call a qualified professional electrician to do the work since you are lacking the needed experience to DIY. If you listen to wood butchers about electrical, you end up with fires.

Splice a new line before the junction box feeding the other lights,then install another box containing your new power line, the feed for the new lights and the new switch line.

In this box connect

a) the white from power to the white of the lights

b) the black of the power to the black of the switch

c) the white of the switch to the black of the lights.

Yes, you need to tap into the incoming electric power to the first switch and from there to your new switch and lights. Now how you want to get the wire from point A to point B is up to you as there are several ways to do it. Your way is probably the easiest.

Turn off the power at the fuse box. Disconnect the power wire from the other switch. Wire both switches with short wires and connect the two wires and the power wire with wire nuts.

you are right already! Just loop a wire from existing switch to new one as dual polarity (Hot to Hot) and run your wire to the new light!

all u have to do is pig tail of off the hot before the switch .and hope that the neutral runs thru the box.because u will have to split the neutral because the new lites are on a separate switch.