As suggested, the Starship Wall mold #301 and the Starship Deck mold #270 should be enough to start, as a minimum. A third mold for "details" would help flesh out the set. I also find the Station Builder mold #300 to be a great source of "plain" blocks. You don't need to have a lot of tiny details on every last piece of wall or item in the room, so these go pretty well with the sci-fi set. I also use them for "blanks" for hand carving custom fieldstone pieces, as well as using them for Roman and Greek architecture, small-scale sci-fi buildings (1:285th scale) and a host of other things.

There are 25/28mm metal Star Wars minis, but they aren't cheap. The plastic "click base" SW figures are a little bit less expensive, but come in "sealed" boxes, so you don't see what you're actually getting until you open the package. Forces fall into "Evil Empire" and "Rebellion" sides, plus a few mercenary or independent figures. Most of the sealed packages contain at least one figure from each side, and I THINK there are something like 5 figures in a box. If you can find a cheap source of the "common" figures, it beats paying top dollar for the sealed boxes in hopes of finding a "rare" figure, which is meaningless unless you're into the insanity of "collecting" the rare ones, like at least 50,000 other kids with too much allowance money. If you just want a few figures for general "play" purposes, you might be able to find someone who is willing to sell off "extras" of the common figs for next to nothing.