The Lizardmen short term goals could be killing any # of the following factions: Chaos (Definately), Skaven (Definately), and possibly the Elves (Both Dark and High, the lizardmen don't see the difference between the two races since their Old one masters originally created them to be on unified race). Capturing territories wouldn't be so much a part of it imo, but if the southlands are added taking the regions there should be a necessity, as well as any rebel settlements (Ruined temple cities infested with Skaven rebels) in Lustria