What Oblivion or Fallout 3 DLC's are they most comparable to? Are they larger additions like say Shivering Isles, or are they some Thieves Den type of stuff? (I'm guessing the 200 MSP one is more similar to the latter.)
They're larger DLCs. Larger than the Fallout 3 DLCs but a bit smaller than the Shivering Isles one in my opinion. Obviously Hearthfire is a smaller DLC. I recommend getting both Dawnguard and Dragonborn. Hearthfire you may or may not like based on how you play. Personally I loved it but some people aren't bothered by it at all but as HoonDing says, you can't really go wrong with how cheap it is.