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
Planned: sLambic II, Flanders Red II, Orange Blossom Mead, Fat Man Porter
Primary:sLambic I, Janet's Brown
Secondary: Toasted Caramel Port, Flanders Red
Kegged: Hefeweizen, Centurion Falcon IPA< Dark Saison
2013 dump volume: ~2 gallons