Start a new game for the Enhanced Edition

I played the first one through and loved it. I'm now playing Witcher 2 and loving it as well.

If your concern is the plot and back-story, I think you'll do fine just reading the plot summary on Wiki

As far as importing a save game, it carries over a little bit of money and gear, but nothing that gives a huge advantage. You'll have earned more money and better gear in a few hours anyway.

The biggest issue I can think of is in understanding the mindset of the character, the game, and the world. The Witchers are powerful warriors like you'd find in other games, but that's not what makes them interesting/unique. Their specialties are knowledge of the many exotic monsters and their alchemy with potions (and traps and bombs in this case).

Reading/researching about creatures would be optional codex/lore in another game, but here it is part of the quests themselves. Potions, bombs, traps would be optional consumables in another game - and I personally rarely use them - but here they're critical.

Many people are struck by the difficulty of the game, and it's usually because they're trying to sword-fight their way through everything. If you really make use of the traps, bombs, potions, oils, etc. you should do just fine.

Lastly, understand that the character Geralt is not trying to be a heroic soldier. Unlike in comparable RPGs, you're neither a great hero nor villain, just something like a tough exterminator travelling from village to village cleaning up their monster infestations. Getting caught up in politics and wars is anathema to the cynical Witcher who just wants to be on his way to the next job.

CD Projekt says they will address the Troll DLC problem in the next patch specifically here.

2. Fixed the free Troll Trouble DLC download. It is now included n the patch so there's no need to download and install it separately

They claim the patch could be available as early as the evening of the 25th (which is like right now).

If you're playing the Steam version, I image you'll have to wait until the patch is rolled into an auto update.

Keep in mind that if you advance beyond chapter 1, the troll quest won't be available on your most current file (at least I can't see how it could be).