With just the core box and a few added figures such as Rebel Troopers and a few more....what map do I plump for first?

Am, I right in saying you only have the maps from the Luke/Vader, then any other expansions you buy at first?

the maps you can get online, you only have the tiles from the core set, the other big sets (twin shadows, bespin, hoth, Jabba, etc ) have additional tiles