If I make a wort using 100% LME do I have to boil it and is there a hot break if I do?
If I make a wort using 100% LME do I have to boil it
No need to boil it. Extract has already been through that process. Not sure how you plan to get your bittering or hop flavor from.
But with extract only wouldn't the beer be very thin - no dextrins?
Malt extract is made the same ways as wort. The difference is that it goes to an evaporator instead of a fermentor, so the sugar composition is very similar to what an all grain brewer would produce.
Briess Amber is 19% dextrins.
http://www.brewingwithbriess.com/Assets/PDFs/Briess_PISB_CBWSparklingAmberDME.pdf
Extracts are made with specialty grains to match common styles:
http://www.brewingwithbriess.com/Products/Extracts.htm#PilsenLight
Cidery flavors are encouraged by warmer than normal temperatures