There is no episode after the Trouble In Tokyo. However there will be a short series called "Teen Titans Go!" in 2013 and if there are enough supporters there may even be a sixth season to the original series.
Terra's first appearance is in Episode 16 of Season 2. Terra's "coming back" is in Episode 21 of Season 2. There are a few more episodes concerning her and *SPOILERS* Slade, but those are in Season 4. Please refer to the link at the bottom of this answer for more.
There may be several episodes in which Starfire drinks mustard, but the first one that I know of was 'The Sum of his Parts', which was Season 1's episode 5, the second and last being 'Mother Mae Eye', which was Season 4's episode 10.