1) 100% chameleon breaks the game. You will be able to kill anything without the enemy fighting back. 100% spell absorb/dmg reflect will make combat boring, but it is effective.
2) Make sure you have 75 armor rating. Fire resistance must be high, other resistances med/high. Try using alchemy to make poisons and/or strong restore pots.
3) Reflect damage. A little bit of chameleon. Elemental shields. Depends on your gear actually.
Shivering Isles is what you can expect of a "larger" DLC. A new exciting questline and landmass to explore

I like Knights of the Nine DLC the most, though.