1.) No, but you want to boil as much volume as you can possibly handle.
2.) Doing a split boil works fine, but it's not a good idea to boil extract that is too concentrated (i.e. not diluted with a sufficient amount of water). That'll result in darkening of the wort and melanoidin or even burned flavors that would be inappropriate for a pale ale
3.) DME should definitely be boiled to sanitize it.
The Fiesty(sic) Goat Brewery est. 2007 & Clusterfuggle Experimental Ales est. 2009
Primary: Saison, Berliner Weisse, sLambic I, sLambic II, IPA, 70/-
Secondary: Orange Blossom Mead, Flanders Red I
Kegged: Fat Man Porter w/ 1469, Fat Man Porter w/ 005, Centennial Falcon w/ Conan, Centennial Falcon w/ Denny's, Barrel-aged Fat Man Porter, Belgian Dark Strong, Dark Mild