I would Like to hang some pendant lights from my ceiling. I want to use this wire. I would only put one bulb (like this) on each length of cord and connect them all to the 12-2 at the ceiling. Is this going to work or will I burn my house down? also is there a limit to how long my cord length can be
18 gauge wire is commonly used in mass-produced lamps. I don't see a problem with using it for single runs of 60w max. It's rated for 7 amps at up to 50 feet. You'll draw about half an amp.
However, the connections you make are perhaps more critical. Be sure to use sound methods when bringing the wires together at the source.
It's safe to do so and there is no limit (in terms of safety) on the cord length.
The 18 gauge wire is rated for 10 amps within 50ft and 7 amps if longer than 50 ft. The LED bulb in your link draws 4W/120V=0.033 amp. (Although it says "60 Watt Equal", it does not draw 60W) So you can wire about 200 such bulbs on your 18 gauge wire without worrying about overheating the wire.
Even if your wire is extremely long, there is no safety hazard. Your device (suppose you wired 200 bulbs) may not get enough power, but nothing would overheat.