Do you currently live in an apartment or a house? I don't think you should upgrade your sub for two reasons; one is that your sub probably is powerful enough for a room that size and two, you are going to be in an apartment and will probably not be able to turn your sub up too high anyways.
That is a good choice for a receiver, you can get them new for $199 on Amazon, but saving $30 is good too.
As for speakers, since you don't want large floorstanding speakers, you are left with bookshelf speakers. I don't know much about specific bookshelf speakers, but you should get some that can produce down to at least 70Hz to ensure you have a solid mid-range with a smooth crossover to the subwoofer. They should also have a woofer size of 5.25" or larger since you have a good size room, if the woofers are smaller they would have to be turned up fairly high to fill the room with sound and this could push your receiver and/or the speakers near their limits and cause distortion or even damage. For the same reason the speakers should be fairly sensitive, a minimum of 89dB sensitivity should be fine.