1. No, they are all very impressive, much more than the "Architecture" sets
2. The whole series
3. A lot of good previous ideas: Kremlin, Sydney Opera House, Colosseum, Big Ben, Golden Gate, Empire State Building, Chrisler Building, Tower of Pisa, Parthenon, Mont Rushmore, White House, Sphinx, San Pietro in Vaticano
4a. A serie of busts from famous actors / character (as the Darth Maul Bust 10018) like Harrison ford / Indiana Jones, Carrie Fisher / Leia, Johnny Depp / Jack Sparrow, ...
4b. An Art serie : La Joconde in Mosaïc, Michelangelo David Sculpture, Bust of Tutankhamun, ...
5. A system to illuminate a model with many LED for a reasonable price