As far as I know, the only expansion set that added new careers was the "Livin' Large" expansion set.
All three expansion sets - "Livin' Large", "House Party", and "Hot Date" add new furniture and objects.
If you have more than one expansion, you typically play the game with the newest of them - but all the expansion material is still in the game. For example, I have all three expansion packs installed. When I play with "Hot Date" though, I still have access to the new jobs of "Livin' Large".
To make your own furniture, you might want to check out other fan sites that do the same. The best starting point is <A HREF="http://www.thesims.com" target="_new">the Sims homepage</A>; I would look at the links under "Get Cool Stuff" and "Fan Sites".
<b>1.4 Ghz AMD T-Bird underclocked to 1 Ghz...just to be safe!</b>