Usually EL wire is hooked up like this:
{Battery/driver --> +- wires --> connector} == {connector <-- +- wires <-- EL wire}
Where I wrote "+- wires" I mean the paired wires that carry power and ground. The connection from EL wire to +- wires is really finicky -- involves stripping the wire without damaging the little 'angel wires'. It's easiest to buy EL wire pre-attached to a wire/connector in the length you need. You can buy 20 foot lengths no problem if you want.
You can join up the +- wires from multiple lengths of EL wire, either by soldering them yourself, or you can get presoldered connectors like
this four-to-one connector from Cool Neon (though I used one of these and only 3 out of the 4 worked, it had a quality issue). You can have any length of wire on each connector. However, the driver has to be sized for the total length of wire you have connected to it. Three 9-ft lengths makes 27 ft of wire -- a little baby driver won't work. Try
this one. In this case it looks like this:
{Battery/ driver --> +- wires --> connector} == {connector -- four-to-one-joint -- 4 connectors} == {connector <-- +- wires <-- EL wire }
.............................................................................................................. == {connector <-- +- wires <-- EL wire }
.............................................................................................................. == {connector <-- +- wires <-- EL wire }
If you wanted to extend EL wire, it could look like this:
{Battery/driver --> +- wires --> connector} == {connector <-- +- wires <-- EL wire --> +- wires --> connector} == {connector <-- +- wires <-- EL wire}
Or like this:
{Battery/driver --> +- wires --> connector} == {connector <-- +- wires <-- EL wire --> +- wires <-- EL wire}
The first gives you flexibility with a connector; the second is permanent, but might look better, since you could make the connecting wire very short. Soldering EL wire can be a pain, again, so it's better to try to avoid it if possible.
There is no good way to split up your power supply to power a 3V light -- the reliable easy option is to have two power supplies, or to have a light that can run on the same voltage as your power supply. Also, if you have a lot of EL wire (27 ft is a fait bit), you might have better results with a 12V power supply (8x AA batteries). Good luck.