I only bought the 32" model in this range, not the 42". The 32" came with the standard 12 months warrenty on parts and labour. There is the option of purchasing extended warranties from LG directly if you want to take out and extended warranty. You can find that link under their support page, which takes you off to Domestic and General Insurance (pretty standard product cover as found in most retail stores in the high street). I didn't opt to get a quote but you can choose to investigate if you're curious.
Hope that helps...
Strictly speaking, no you don't need a 3D blu-ray player to use the Cinema 3D function, but it would be a good idea to get one. If you have Sky HD then the 3D channel can be added for free, but that is only one channel. There is a 2D to 3D conversion mode but it is not as good as a true 3D broadcast program.
3D blu-ray players are not that expensive now, I already had a PS3 which can play 3D blu-rays so I didn't have to buy one. At the end of the day it's your choice but I would recommend it to get the most out of the TV's 3D ability.
With regard the Dual Play, yes it does have it built in, this model does not come with the glasses supplied for the Dual Play (they are different to the normal 3D glasses of which you get 4 pairs) but are easily available from various suppliers.
Hope this helps.