Should be fun for you. Yes, best to go back and finish up S4, at least through the one that has River in it. You can probably skip out on the end and most of the specials, picking up with Waters of Mars and The End of Time. That way you can skip what happens to Donna in the end. (Grr.)

I'm not as much on the Silurians episode, but that might be because I hate the accurate lesson of both of those episodes.